Countries with the youngest and oldest populations

- Median age: 42.3 years
- Fertility rate (births per woman): 1.49
- 2020 population: 441,543

Malta’s population has more than doubled since 1911 when the country was home to 211,564 people. Malta has the lowest fertility rate among European Union countries, with 1.23 children.

- Median age: 19.7 years
- Fertility rate (births per woman): 3.52
- 2020 population: 12,952,218

A full third of Rwanda’s population is younger than 30. More than half of the country was born after the Rwandan genocide in 1994.

- Median age: 42.5 years
- Fertility rate (births per woman): 1.38
- 2020 population: 19,237,691

The ratio of those in Romania 65 and older is less than the European Union’s average—yet day-to-day life for the elderly gets some of the lowest marks throughout the union, according to a 2018 Eurostat report. The study found 17.2% of elders living alone in 2018 couldn’t heat their homes; with just 23.4% of those older than 65 rating their overall health as good or very good.

- Median age: 19.6 years
- Fertility rate (births per woman): 4.44
- 2020 population: 1,318,445

For such a young nation, Timor-Leste faces a wide variety of challenges. After gaining its independence in 2002, the country has struggled to face down its economic woes. With more than two-thirds of the country younger than 30, there is a marked tension between the high number of young people and the demand for jobs.

- Median age: 42.7 years
- Fertility rate (births per woman): 1.57
- 2020 population: 8,654,622

Education is important in Switzerland: 87% of adults have completed upper secondary education, which is optional. A 2008 Harvard study linked an increase in education to a longer life span, reporting that even a single year of college can lead to an extra 1.6 years of life. It's not necessarily the classroom learning that adds length to your years, but rather the elevation of your socioeconomic status through education. It may be the case in Switzerland that a focus on higher education is leading more people to live longer, increasing the country's median age.

- Median age: 19.5 years
- Fertility rate (births per woman): 4.82
- 2020 population: 38,928,346

Afghanistan has one of the lowest life expectancies in the world. The country, which has been at war since 1979, has not only lost more than 1 million lives to the conflict, but also has limited electricity—according to the Huffington Post, only 6% of residents have access—limited access to safe drinking water, and poor sanitation. Afghanistan is also one of the largest opium suppliers in the world, and the violence that surrounds the drug trade makes the country notoriously unsafe.

- Median age: 42.8 years
- Fertility rate (births per woman): 1.77
- 2020 population: 17,134,872

Those who have visited the Netherlands know just how quintessential the bicycle is to this nation's way of life. Amsterdam alone is home to more than 1 million bicycles. Regular physical activity, which raises your heart rate over its resting rate, has been linked to longer life, according to the National Cancer Institute.

- Median age: 19.4 years
- Fertility rate (births per woman): 4.04
- 2020 population: 16,743,927

In Senegal, 38.2% of the adult population is illiterate, and only about 73% of children are enrolled in primary school. The country's general approach to education means that many aren't able to advance their socioeconomic status in this manner. Many Senegalese aren't able to access life-saving health care, and more than 1 million households go without basics like electricity. Both of these factors are likely to contribute to a shorter life expectancy in Senegal.

- Median age: 42.8 years
- Fertility rate (births per woman): 1.74
- 2020 population: 5,540,720

Finland is one of the best-educated countries in the world. A full 88% of adults have completed an upper secondary education. Better educations mean longer lifespans, both because education helps to elevate a person's socioeconomic status and because it prompts individuals to lead a healthier, less-risky lifestyle.

- Median age: 19.1 years
- Fertility rate (births per woman): 4.92
- 2020 population: 13,132,795

Out of the top 10 leading causes of death in Guinea, nine are related to health. From influenza to tuberculosis to malaria and HIV/AIDS, the country's poor health care system isn't equipped to handle the needs of the country's nearly 12.4 million residents. In fact, 10–15% of citizens can't afford health care, and there is no public system in place that ensures they receive even the most basic medical attention.

- Median age: 43.3 years
- Fertility rate (births per woman): 1.33
- 2020 population: 3,280,819

Bosnia and Herzegovina lies on the Balkan Peninsula in southeastern Europe. The country is small in size, but its residents are close. Family ties are strong in Bosnia and Herzegovina, and a major emphasis is placed on friendship and neighborhood communities. The strength of these social relationships could be doing a lot in regards to the age of the country's population, according to Harvard Health: People who have satisfying relationships with family, friends, and their community are happier, have fewer health problems, and live longer.

- Median age: 19.1 years
- Fertility rate (births per woman): 4.62
- 2020 population: 7,976,983

The average life expectancy for someone born today in Sierra Leone is just 58.5 years old. A Lancet study published May 12, 2020, estimated that disruptions to health care because of COVID-19 could cause 1.15 million child and 56,700 maternal deaths around the world before 2021, with countries such as Sierra Leone being disproportionately affected.

- Median age: 43.4 years
- Fertility rate (births per woman): 1.46
- 2020 population: 8,737,371

Neighboring Bosnia and Herzegovina, Serbia has had a difficult and war-torn past, but the median age in the country is still well above average. One possible reason for this is that, just like Bosnia and Herzegovina, the country places a strong emphasis on social and family ties as well as marriage. As discussed before, stronger relationships can improve overall health, leading to longer lives.

- Median age: 18.6 years
- Fertility rate (births per woman): 4.72
- 2020 population: 206,139,589

Many factors contribute to Nigeria’s young population: Terror groups like Boko Haram, which killed 900 people in 2017, millions living below the poverty line, inadequate health care (HIV/AIDS and malaria are the two biggest concerns), air and water pollution, and malnutrition are the primary culprits.

- Median age: 43.6 years
- Fertility rate (births per woman): 1.47
- 2020 population: 9,660,351

The OECD ranks Hungary as well below average in many of the factors it considers, like average income, employment, education, community, and health. But one place the country comes up above average is its work-life balance. While an improved work-life balance isn't linked directly to a longer life, it is linked to a lower rate of chronic stress—which can lead to things like hypertension and heart-related conditions—as well as fewer mental health afflictions, which can lead to suicide. One reason the median age is so high in Hungary could be that Hungarians are overall healthier than many other nations, thanks to their above-average work-life balance.

- Median age: 18.6 years
- Fertility rate (births per woman): 5.54
- 2020 population: 11,193,725

South Sudan is the world's youngest state, having just established its independence from Sudan in 2011. The civil war that helped South Sudan gain independence is still ongoing, and many are losing their lives to violence. Little aid for humanitarian workers and a rising risk of famine also keep life expectancy short.

- Median age: 43.7 years
- Fertility rate (births per woman): 1.69
- 2020 population: 38,128

Liechtenstein is a small German-speaking principality between Austria and Switzerland. Of all the European countries, Liechtenstein has one of the highest wage levels and one of the lowest unemployment levels. It's probable that this high income has something to do with life expectancy. Financial stress has been shown to lead to earlier deaths and more health problems, so it's fair to infer that those steering clear of added stress and all of its negative benefits are living longer in large part thanks to their financial security.

- Median age: 18.5 years
- Fertility rate (births per woman): 4.66
- 2020 population: 26,545,863

According to a report by World Health Rankings, the leading cause of death in Cameroon is HIV/AIDS. As of 2017, there were half a million reported cases of AIDS, representing 3.7% of the country's population. A lack of education about the disease and medical treatment are both possible reasons HIV/AIDS remains so widespread and continues to cut lives short.

- Median age: 43.7 years
- Fertility rate (births per woman): 1.61
- 2020 population: 1,326,535

There are many factors in Estonia that seem as though they should have a negative effect on the country's average lifespan. For example, life satisfaction is low, overall health is down: 25% of Estonians are at risk of getting cancer before the age of 75, and income is just about half of what the OECD considers average.

- Median age: 18.5 years
- Fertility rate (births per woman): 5.51
- 2020 population: 15,893,222

The Somali Civil War began in 1991 and has yet to find a resolution. While some think it's getting closer—a 2017 election, albeit riddled with corruption and violence, was seen as a major stepping stone—others think there's still a way to go before reaching the end. An estimated 1 million Somalis have died as a result of the conflict, which is arguably the main reason for the country's young population.

- Median age: 43.7 years
- Fertility rate (births per woman): 1.49
- 2020 population: 6,948,445

Genetics plays an important role in life expectancy. Genes determine our susceptibility to diseases like cancer and diabetes. Bulgaria, adjacent to Greece and Turkey, has a well-below-average rate of cancer incidences and mortality, and only 7.9% of its population has diabetes—statistics that would seem to indicate that their strong genetics play a large part in the high median age in the country.

- Median age: 18.3 years
- Fertility rate (births per woman): 4.72
- 2020 population: 43,849,260

The Darfur genocide, in which Darfuris living in Sudan were murdered on the orders of the Sudanese government, began in 2003, resulting in the death of 400,000 Dafuris and displacing 3 million others. The fighting and political unrest that followed led to even more lost lives. All told, this may be part of the reason behind the country's young population.

- Median age: 43.9 years
- Fertility rate (births per woman): 1.51
- 2020 population: 46,754,778

Spain is well above average in two categories most directly linked to a longer life: community and happiness. General feelings of happiness tend to lower the levels of the stress hormone cortisol in the body and decrease overall inflammation. They also tend to be indicative of a person who has strong relationships and a sense of general well-being. So it's quite possible that the population in Spain lives longer simply because they're happier.

- Median age: 18.0 years
- Fertility rate (births per woman): 4.75
- 2020 population: 1,968,001

Guinea-Bissau is currently facing a host of environmental issues, many of which may contribute to the young median age in the country. Only 8.2% of the land is farmable, which has caused a food shortage, leaving 17% of the country's children underweight. Deforestation, overfishing, and soil erosion are other major problems the country faces, leaving many families under the poverty line and lacking sufficient nutrition.

- Median age: 43.9 years
- Fertility rate (births per woman): 1.42
- 2020 population: 4,105,267

It's no secret that pollution has an effect on our lives. A 2018 study published in Science shows that air pollution shortens lives by more than a year, and water scarcity and quality certainly have an effect on lives as well. Croatia has low levels of air pollution, and its water quality is generally high.

- Median age: 18.0 years
- Fertility rate (births per woman): 4.90
- 2020 population: 5,057,681

A 14-year-long civil war has made life difficult in Liberia. Currently, 75% of Liberians live on $1 per day or less, meaning that many are suffering from malnutrition, have no access to basic health care, and have no piped water or electricity. All of these things are probable contributors to the short lifespan and young population in the country.

- Median age: 44.4 years
- Fertility rate (births per woman): 1.53
- 2020 population: 1,886,198

Strong family ties are likely to be one of the major factors in the long life expectancy for Latvians. A 2016 study by the University of Toronto's School of Public Health demonstrated that the family relationship, more than any other relationship, was essential for adding years to one's life—especially for older people. Those who listed family members (or spouses) as their closest confidants only had a 6% risk of dying over the next five years, while those who listed other people, like friends, had a 14% risk. The family is still the center of the social structure in Latvia, where multigenerational homes are common.

- Median age: 17.9 years
- Fertility rate (births per woman): 4.51
- 2020 population: 20,903,273

Burkina Faso has never been considered a safe place to live, but in recent years the violence has gotten worse. More extremist religious groups have popped up in the area, and the uptick in terrorist attacks, combined with the major criminal networks that already plague the country have made this a place that the OSAC recommends foreigners don't visit. The levels of violence may be one reason the population is so young.

- Median age: 44.5 years
- Fertility rate (births per woman): 1.60
- 2020 population: 2,722,289

Lithuania has one of the highest marriage rates in the European Union. Interestingly, marriage was one of the first nonbiological factors associated with longer life. It turns out that married people take fewer health risks, have better physical and mental health, and have more emotional and material support. So it's possible that the high number of married couples in Lithuania is a contributing factor to the older median age.

- Median age: 17.7 years
- Fertility rate (births per woman): 5.28
- 2020 population: 11,890,784

The Burundi civil war lasted from 1993 to 2006. It is estimated that 300,000 were killed during the conflict and an additional 1.2 million more were displaced. This alone lowered the median age in the country by a significant amount. Additionally, three-quarters of the population live in poverty, relying on international aid groups for housing, jobs, and medical care. New rules requiring a certain ethnic balance in these aid groups have many pulling out of the country, meaning that it's likely the median age here will continue to drop.

- Median age: 44.5 years
- Fertility rate (births per woman): 1.49
- 2020 population: 9,006,398

Austria has a reputation for being a relaxed country. Work is not a top priority here, and while most people are employed, many businesses close early and for long stretches of time in the summer, providing a great work-life balance. Austrians also walk and bike most places they go, rather than relying on cars, which keeps them physically fit. Finally, Austrians report an above-average level of life satisfaction, which has been linked to longer lives.

- Median age: 17.0 years
- Fertility rate (births per woman): 5.53
- 2020 population: 12,123,200

Poverty remains the biggest issue facing Benin today. While life in the country's main cities and urban areas has improved, those living in remote villages still struggle with a lack of electricity, poor sanitation, limited access to clean drinking water, and little to no basic medical care. These things could all be factors that contribute to the country's low median age of 17.

- Median age: 44.6 years
- Fertility rate (births per woman): 1.41
- 2020 population: 10,196,709

Portugal is another country with low pollution levels. Air pollution and water pollution here are both lower than average. Air pollution, in particular, has been linked to cardiorespiratory diseases and lung cancer. So it's logical that a country with less air pollution would have fewer cases of these diseases, and would be healthier overall, which would lead to an older median age of the population.

- Median age: 17.0 years
- Fertility rate (births per woman): 4.97
- 2020 population: 31,255,435

More than 2 million people in Mozambique were living with AIDS in 2017, with 70,000 deaths annually contributed to AIDS. For a country with a population of just over 31 million, this is a staggering ratio. It may also be a major reason that life expectancy and median age are so low in the country.

- Median age: 44.9 years
- Fertility rate (births per woman): 1.59
- 2020 population: 2,078,938

Slovenia has two things going for it that may be major factors in the longer life expectancy of its citizens. First, their education system is highly ranked, and 87% of adults have completed upper secondary education. Second, Slovenians spend a lot of time outdoors: Hiking, biking, kayaking, and skiing are all common leisure activities, and this level of physical exercise most likely goes a long way in keeping them healthy.

- Median age: 16.9 years
- Fertility rate (births per woman): 5.49
- 2020 population: 18,383,955

A land-locked country in sub-Saharan Africa, Zambia is home to 14 million people and surrounded by other countries on this list: the Democratic Republic of Congo, Angola, and Zimbabwe. This country is a poor one, with 64% of the population living on a dollar a day or less. The extreme level of poverty leads to other things, like the fact that 14% of the population has HIV and no access to medical treatment, and 40% don't have access to clean water. Both of these factors may be reasons that the country's median age is 16.9.

- Median age: 45.2 years
- Fertility rate (births per woman): 1.52
- 2020 population: 33,931

Officially considered a “microstate,” San Marino is surrounded on all sides by Italy. The food the Sammarinese eat could have something to do with why they live so long: Their diet is largely Mediterranean, relying on olive oil, fish, vegetables, and whole grains for nutrition.

- Median age: 16.8 years
- Fertility rate (births per woman): 5.31
- 2020 population: 19,129,952

Malawi is one of the smallest countries in Africa, with one of the highest populations. An estimated 18 million people live here, but only 1 in 10 has access to clean water. Severe flooding in 2015 contaminated many of the trusted water sources, and insufficient infrastructure—as well as a series of droughts—have made it difficult to fix the problem. The lack of drinkable water may be a factor in Malawi's limited life expectancy.

- Median age: 45.3 years
- Fertility rate (births per woman): 1.38
- 2020 population: 10,423,054

Studies have shown that following a Mediterranean diet can help you live longer. Diets that are low in meat and dairy, high in fruits and vegetables, and low in refined carbs can keep life-threatening medical conditions like diabetes and heart disease at bay, adding a year or more to your life. A 2005 study published in the British Medical Journal found that this was especially true of those living in Greece, as they follow the Mediterranean diet closely. This could be a leading reason that the median age in this country is so high.

- Median age: 16.7 years
- Fertility rate (births per woman): data not available
- 2020 population: 89,561,403

The Democratic Republic of the Congo has the third lowest GDP per capita in the world: $800 (according to 2017 estimates). Not only is the country extremely poor, which is directly linked to a shorter life span, but decades of war and violence have claimed the lives of millions and displaced an estimated 4.5 million people. Other things like a lack of education, a shortage of income-generating employment opportunities, and almost no health care are also believed to be major factors in the country's low median age.

- Median age: 46.2 years
- Fertility rate (births per woman): 1.43
- 2020 population: 77,265

Andorra is a small principality situated between France and Spain, that's primarily known for its ski resorts. It's also a perfect blend of nearly all of the major contributing factors of longevity. The health care system is outstanding, wages are higher than average (which correlates to increased socioeconomic status and healthier habits), the air is free of pollution, the water is clean, and the country places a large value on education. Students boast a 100% literacy rate, as education is free, of high quality, and easily accessible.

- Median age: 16.1 years
- Fertility rate (births per woman): 5.68
- 2020 population: 16,425,864

Ever since establishing its independence as its own country in 1960, Chad has been in a perpetual state of unrest. In 2005, the country fell into its fourth civil war, largely thanks to the conflict taking place in neighboring Sudan. Between lives lost to fighting and violence, and those lost to the other ravages of war such as famine and disease, life expectancy in the country has yet to improve.

- Median age: 46.5 years
- Fertility rate (births per woman): 1.47
- 2020 population: 60,461,826

As of 2016, the average household income in Italy was 30,595 euros (around $34,681), making Italy a notably wealthy nation as a whole. Wealth has been tied to increased longevity, primarily because it indicates better health and nutrition literacy, and access to better nutrition. One reason Italy's life expectancy and median age is so high could be their relative wealth, and the quality of life that provides.

- Median age: 16.0 years
- Fertility rate (births per woman): 5.72
- 2020 population: 20,250,833

Mali has been in the midst of a major political crisis since 2012. Ethnic violence and differences between religious extremist groups have been the main instigators of the civil-war-like conflict. War shortens life expectancy, but new research shows that survivors' life expectancy may be shorter as well. Post-traumatic stress disorder has been linked to faster aging and earlier death; University of California San Diego researchers in 2015 concluded that PTSD increased the risk of dying by 29%. This could be one of the factors accounting for the young population in Mali.

- Median age: 47.8 years
- Fertility rate (births per woman): 1.47
- 2020 population: 83,783,942

Seventy-two percent of Germans qualify as middle-class while 75% between the ages of 15–64 are employed. Additionally, 86% of adults have completed upper secondary education and 92% of people believe they have someone they could rely on in a time of need. This means that most Germans are educated, relatively wealthy, receive quality health care, and have strong friendships and relationships. All of these are likely reasons that the country has one of the oldest populations in the world.

- Median age: 15.9 years
- Fertility rate (births per woman): 5.96
- 2020 population: 32,866,272

Angola spent three decades in a civil war. While the war officially ended in 2002, many of the effects still linger. For example, malnutrition for both children and adults is a major concern in the country. The lack of proper nutrition and the sheer amount of deaths caused by lack of food is likely one of the leading factors in the short life expectancy for residents.

- Median age: 48.6 years
- Fertility rate (births per woman): 1.43
- 2020 population: 126,476,461

Plenty of studies have been done on the negative effects of Japan's work culture, which is considered extreme at best. And while it seems that the added stress and poor work-life balance would make lives shorter, Japanese people actually have the second-longest longevity rate in the world. Two things may account for this: the traditional Japanese diet, which contains lots of vegetables, fish, and few processed foods, and the emphasis placed on education—99% of Japanese adults are literate, and Japan has the second-best education system in the world.

- Median age: 15.7 years
- Fertility rate (births per woman): 5.54
- 2020 population: 45,741,007

Uganda is a quickly developing country. However, the nation still struggles with education; partially due to the large refugee population and to the lack of educational funding. Only 73.8% of adults are literate, and fewer than 25% of children move on to secondary school after completing primary school. A lack of education, which keeps them from moving upwards in the socioeconomic strata, may be a large factor in the country's young population.

- Median age: 55.4 years
- Fertility rate (births per woman): 1.55
- 2020 population: 39,242

The country with the oldest population in the world is Monaco. A sovereign city-state on the French Riviera, one in every three people living in the country are considered millionaires. Their taxes help support a top-notch health care system, featuring hospitals and clinics with the most modern technology available, and safe water and sanitation for all citizens.

- Median age: 14.8 years
- Fertility rate (births per woman): 7.00
- 2020 population: 24,206,644

Niger is the youngest country in the world, with a median age of 15.5. There are hundreds of different factors that contribute to this fact, but one could be the high number of average births per woman. Scientists have found that women who have given birth have biologically older cells. The high number of births may be aging women prematurely, causing them to die sooner.