How to gracefully decline alcohol/other substances?

I turn 21 this year and already people are making comments that I can buy alcohol soon. I have no intention of ever doing so. My entire family, consisting of 4 aunts, 4 uncles, and lots of cousins, the only non-alcoholics are me and my parents, and they're both former alcoholics. I love my family very much, but all family activities focus on alcohol, or worse. I dabbled a bit trying to fit in but decided it wasn't worth what would obviously eventually happen. Four have been to jail for alcohol in the last year alone, and one very narrowly avoided it-the rest are just better at not getting caught. I've also pretended to be doing it a couple times, but I can't always get away with pouring out the beer or not actually inhaling, plus once I turn 21 what do I do when I get asked to go hang out at bars? I'm deathly afraid of ending up like the rest of my family, but I don't want to say THAT obviously