21 is pretty sweet! You can drink alcoholic beverages (legally) now! Also, if you're in Arkansas, you're finally old enough to breathe in second hand smoke indoors (the Clean Air Act we have here is incredibly stupid). I'm 22, but I still get a kick out of ordering a beer or a margarita at restaurants. I don't eat out at non-fast food restaurants often though, so it's still sort of a novelty to me.
So yeah, be sure have fun with it!