Thought I'd point out that the whole "college students don't own cars" thing is really only applicable to Madison and the Isthmus' crazy parking situation.... and maybe urban colleges like those in Milwaukee, etc. Many other college towns (i.e. Purdue, UIUC, and especially commuter colleges like Whitewater, etc) often have acres of low/no cost parking for students and I think car ownership is more prevalent or even necessary to make grocery runs, etc.
I personally think things are OK as they are. I think it's good for teenagers to drive as it prepares them for adulthood and independence. As a dad with teenagers at home, I can tell you chauffeuring teens around is the pits and encourages an entitlement/dependence mentality....we had to really push for our 16-year old to get her license just because we were sick of taking time out of our day to drive a perfectly able-bodied person to school everyday, work, activities, etc (believe it or not, many younger millenials care little about driving privileges and are perfectly happy to be chauffeured around....the fact that someone had to be inconvenienced for them to get where they want to be is often inconsequential to them).
The 21 drinking age certainly doesn't deter all underage drinking but from my experience was a decent enough barrier to make all day / everyday partying less likely.