In my estimation, prohibiting minors from drinking and restricting the sale and advertising of alcohol only creates a forbidden fruit that encourages young adults to develop drinking problems.
You are correct. When I was young, one of the most exciting things we did was find somebody to buy us a case of beer so we could go into the marshes and get drunk. As soon as I got old enough to purchase beer legally, it was no big deal and I rarely got drunk again (and haven't been for nearly 15 years despite having at least a beer or two daily). You see, when alcohol was "forbidden", you tended to overindulge when you got it because you didn't know when you would get it again. Ironically, at the very time when we needed adult supervision, we had none because an adult could be arrested by the police if we drank in their presence. So we had to take our case of beer and hide. When we got old enough to drive, you can imagine the hairy incidents we got ourselves into. I was very lucky as a teenager to have avoided death, injury or serious trouble with the law. Others I knew weren't so lucky.
Over in Europe (look out, here will come the people who say "So you want to be just like Europe, huh?"), children are allowed to drink with their parents and are thus ready to drink responsibily themselves at a much younger age than over here. No, I don't want the USA to be "just like Europe" but that doesn't mean that Europe doesn't do a thing or two better than us.
Parental supervision is so key to teaching a child to drink responsibly. When we teach our children to drive, we don't force them to go driving alone with their friends, who are also inexperienced. No! We spend many hours in the car with them, teaching them all the ropes. Yet when it comes to alchohol, we turn a blind eye and force them to go off into the woods by themselves with their immature friends to get blotto drunk. Why are we so stupid about this issue?