People are drawn in to the fact that something is considered "taboo", more often than not. I was arrest with 11.6 grams if Ganja, 3 years probo, 200 hours community service etc. When I'm off I am moving to Colorado where it is legal, as I use it to self medicate.
Underage drinking is more common only for the fact that alcohol is so much easier to get. Just get a friend who is 21 to buy what you want. Kids love to get fucked up, which is not exactly right, but it's true. I'm not huge on alcohol myself, a couple beers are okay but I hate getting wasted.
As for other recreational drugs, it really depends. MDMA and Acid are a part of my culture. I've been a ravechild since I was twelve, though I haven't done either of the former until I was eighteen, and I very seldom did those chemicals.
There's a lot more into it than a simple factor of breaking the law.