Age doesn't really matter, if the clothing you wear looks good on you and you're comfortable enough with yourself to wear it, why not.
I prefer seeing a 50 year old looking good in a mini skirt than an 18 year old in low cut jeans with a muffin top.
EDIT: I've also seen girls with low-cut jeans pulling them up about twice a minute.
If you don't want to show your ass-crack, choose different jeans or wear a belt.
Pulling them up all the time only draws attention.