Happy birthday, man! Enjoy it...
It has now been more than half a lifetime ago, but I'll never forget my 21st birthday. It involved some rather heavy drinking and a fair bit of puking in the morning. Unfortunately, I was a grad assistant and had to teach at 8am that morning (my birthday was on a Friday, but my friends insisted that I have my first drink at the stroke of midnight which meant that they dragged me out on Thursday evening). It wasn't pretty that morning, trying to teach accounting on 3 hours of sleep, and (effectively) still drunk.
Never again, but I'm glad I did it. You only live once.