^^ bit of both on this. Cars are just cheap in the US and thus lend them to a younger buyer (in general). Z4 is though expensive car and is the main reason you dont see too many of them. 35iS here in Geneva when new my car was 104k CHF, thats 112k USD, making it substantially more than in the US.
I just hit 35 a month ago so thus 35 was my answer. Would i have had 112k USD to blow IN CASH (dont do credit) when i was 25, probably not. Not only does online tend to make ages skewed and rightfully so, Americans (in general) are more about instant gratification and would prefer to buy a nice new car but have no money for gas.
I lived in Dallas for 6 months after under-grad at UT Austin. We called the people 23-25 30,000 dollar millionaires. Brand new 70k car, maxed on a loan and not but 5 bucks in their pocket for gas till the next paycheck.