Not quite. Drinking, yes. But local municipalities are free to pass regulations about clubs and such. For example, here in Champaign County, you have to be 18 to get into a bar, but in the City of Champaign, while Urbana has no law, so it's 18 there. You have to be 21 to drink, but only 19 to get in.
There is kind of nod-nod wink-wink between the bar owners and the local politicians though; they could eliminate underage drinking in a heartbeat if they wanted to; all they'd have to do is start fining bar owners if they found minors in possesion of alcohol, and raiding the bars once a week. But the local gov't knows that a LARGE percentage of their liquor tax revenue comes from underage drinkers. And bar owners know a large ammount of their profits come from underage drinkers.
So they raid sporaidicly, handing out a few drinking tickets here and there just to students. Bar owners win, city wins, students get to drink underage pretty freely, but will get screwed when caught.
Like I said, the letter of the law is 21. How well it's enforced is a different matter entirely.
Happy contrails - I support B747Skipper and Jetguy