I have the same problem, I'm 26, but I'm only 5'1 and I just don't look that old. Bouncers ALWAYS check my ID twice, I have no problem if I pay the bus the child rate.... etc etc.
My rules for looking a bit older
1: Wear anything but jeans, or if you wear jeans, only wear them with heels and a nicer shirt.
2: Wear make up
3: if your hair is long, when you want to look older, put it up
4: Wear glasses if you have them
also to go along with smoking and tanning, try getting no more than 3 hours a night of sleep for about a week or so, that'll make you look a bit older as well.
