Having grown up in Milwaukee, where the legal drinking age is 12, particularly if you hang out with musicians, I think I had a really dull 21st as the novelty of being able to drink had worn off.
I make it a point to spend my actual Birthday working on something, art or a project, I grandstand so much in my daily life that being the center of attention makes me uneasy.
Whoop it up on your 21st, just be sure to do it with people you really like, and don't feel compelled to make yourself violently ill, nothing worse than that next morning.