I tend to agree aith 16 being "too young" to drive. My daughter started driving a year ago. And I was more than a little "frightened" when she got behind the wheel the first time. Still, as her parent, I could have insisted that she be 18 before she started driving.
I remember when the drinking age, in many states, for beer was 18. There were some problems with highschool seniors going out at lunch and legally having enough drinks to come back to school essentially "drunk." So it's not an easy issue. That being said, 21 seems a little odd given the fact we have soldiers who have had to shoulder the horrors of war yet not be able to "legally" take a drink. America is a land of enigma.