Well, happy birthday! 20 is a good age...enjoy it.
And as for 21, it'* not a big deal really...the fun is looking forward to it when you're 20.
I am 22 now (23 August 27th
), and there are no more big birthdays for me, but 21 never felt much different than 20 anyway. I'll admit that I've never been much of a drinker, but even for my friends who got wasted all the time before they hit 21, once they hit legal age it lost its appeal.
I'm just glad to be done with the hassles getting ammo. :P