i started drinking on occasion as a kid, as my dad made me drink to the bottom of his martini when i wanted to eat the olive. we also got to drink sometimes on family camping trips.
once i was 14 or 15 my friends and i began drinking recreationally. we would each steal some liquor or beers from our parents, save it up for a while, then put everything together and party. we also loitered around liquor stores hitting people up to buy us beer. we got rejected a lot and flat-out burned by someone just taking our money one time, but you learn who to ask and who to not bother with.
quite a few homeless people in the area had bought our beer at some point. as long as you throw in a couple dollars for their trouble, bums are usually pretty cool about buying alcohol for you.
in response to the peripheral issue in this thread, i agree that the drinking age in america should be lowered to 18. you're legally an adult at 18, can vote, can join the military, etc. but you can't buy a simple beer. however, i also think the driving age should be raised to 18.