No, I was 23. But still, the idea.
I've seen "Must be 21 or able to beat up the bouncer to drink here" signs.

EDIT: There's a long tradition, in my hometown at least, can't say about other places, that if you're old enough to be in the military (Militia counts), you're old enough to drink. Show your military ID, and, unless the Inspectors are being dicks that week, you're in.