Old thread, but so what!
I first started drinking when I was 12, so the thread caught my attention. I didn't have any friends at the time, so my drinking consisted of sneaking liquor from my parents' cabinet and replacing it with water. Then, in high school, I upgraded to chugging bottles of cooking wine, which were sold as a cooking ingredient in the Italian aisle, and were not age-restricted. To deceive the cashiers, I'd also pick up spaghetti and pasta sauce when buying it; then after paying, I'd dump everything but the wine into a food pantry donation box. I kept using this method all the way until I turned 21 (the US drinking age). After turning 18, I supplemented the cooking wine with cigarettes, since the smoking age is 18.
One thing for sure: DO NOT drink with people you don't trust. OP, it sounds like you don't trust your alleged "friends" here, so find a new drinking group, if you must drink at all.
And while I'm sure I'll get eaten alive for saying this, but I don't think there should be a drinking age. Alcohol helped me get through REALLY difficult times when I was young and powerless. Also, some of the most disgusting, cruelest people I've met were non-drinkers, and very self-righteous about it to boot. Which is why I'm not being all preachy against alcohol. Except one thing: NEVER get into a car with a drunk driver.