Steve gives some very good advice which I don't need to repeat.
The only thing I would add to it, is that I truly feel that drinking is WAY overrated. It's entirely too common for teenagers to drink because it's taboo and they usually do it for the purpose of getting drunk.
No one argues that drinking kills brain cells... so I would ask this question: Knowing that alcohol kills many brain cells when you drink, why drink during a time in your life when your brain is still developing? (I'm sure Anyee can speak very specifically to brain development in teenage years)
Of course, it's all about "freewill", but still...