Went with a group of eight 21 year olds this summer and driving licences were fine everywhere we went. And yes, you get ID'd everywhere you go. Also, if you go to a liquor store, they'll ID anyone they see.

Not that I'm advocating it but you'd probably get away with fake IDs. I've heard most of the kids out there use them and with a foreign one they're less likely to know what to check for.