I did most of my drinking before I was 21. What's this "back-alley" nonsense? There was always someone with alcohol or who could get it. There are alot of legal adults that don't mind drinking for free.
Another good point. I had 20 times the access to alcohol in High school than I did illegal drugs. Both were illegal for me to buy, but why was alcohol sooo much easier?
Because it is a legal substance. Do the same with hard drugs and they would become 20 times more accessible to high school kids.