If she's legal in your country - and age of consent is 16 in some countries, Canada, for example, and probably at least a few European countries, you're okay from the legal point of view.
As drinking goes, fuck, every teenager drinks and there's pretty much no way you could get in trouble for that unless you're also causing public destruction and being overly noisy. The laws on legal drinking age are retarded in some countries, like a whole lot of USA states. You can drive, you can become a soldier and be in a warzone where your job involves killing and being killed, but you can't enjoy a drink? That's idiotic.
So, assuming you live in a country where she's legal, I'd say there's nothing wrong with it. That, assuming that I didn't misunderstand what I thought was a hint in your message.
Otherwise, if she's a cool person some 4 years difference shouldn't play a big role in friendship and stuff. You don't have to fuck every person you hang out or drink with.
If I'm right on my assumption along with a good portion of the posters in the thread, don't count on a relationship either way. Seriously. If you're an adult (aka above 18, possibly living away from home etc) why the HELL would you want to date someone who is still under almost complete control of their parents?