There was an article in TIME magazine about this a while back, that aired some of the same views here. :]
I believe that safe and responsible drinking is the duty of the parents to teach to their kids. Everybody knows that drinking goes on in a college campus, and someone who thinks otherwise is somewhat of a fool. If the parents don't teach their children to drink, then who's supposed to do it? Their teachers? Their friends? That's definitely not right.
I don't think there's anything wrong with parents giving their kids a sip of wine at the table every now and then, if they ask. If it's made so forbidden, and they hear from their friends that drinking / partying is so fun, of course a lot of kids will at least think about trying it - and that's not even talking about those who actually go out and do so. Yes, you're right - at 18, there might be quite a few people who aren't ready to drink because they lack maturity. Why, then, the double-standard - you're old enough to be drafted and enlist in the military, but not old enough to drink? You're responsible enough to smoke (which, by the way, is also pretty unhealthy in irresponsible amounts), but not responsible enough to know when not drinking is better? That smacks of... well, I'm not sure what the word is, but the "18-year-olds aren't responsible enough to know what's right" statement just doesn't apply all the way across the board, and it should.
Anyway. I think it should go ahead and be lowered. If people really want to, they'll find a way to get alcohol anyway - might as well just make it legal, and perhaps establish some more visible ways to warn students about alcohol poisoning and the dangers of binge drinking, and how it can ruin your health and future.
I definitely agree with Ruby, though - it's the parents' job to prepare their kid to go into the "real world".