It's not as though younger credit card users are spending more than others because of outright consumerism — there are other expenditures at play, as mentioned previously.
Auto costs, for example, don't discriminate by age or financial situation: A Toyota Camry costs as much for a 30-year-old driver earning $50,000 a year as someone who is twice as old and earns twice as much. Experian data shows that younger and older drivers owe similar amounts on the auto loans they carry, which isn't the case for most other types of consumer loans.
Indeed, if anything, age and credit conspire to make the costs of driving and insurance for a Camry more expensive for those just starting out: Premiums tend to be higher, and credit scores lower, than for older drivers. (Take heart; at least gasoline still costs the same for combustion engine drivers of all ages.)
Younger consumers tend to be renters as well. Unfortunately for those living in faster-growing metros, the rental inventory doesn't always keep up with the population growth.