Personally i don't think theres any magic age. I love love love makeup, but that doesn't mean i wear it every day. I usually only wear mascara and do the fullface only if i'm going out or doing something special. if you don;t have any skin issues sometimes makeup can cause more problems then anything. lots of foundation and coverup and powder on your face can cause breakouts. I started wearing my mom's and sister's makeup when i was about 11 or 12. in secret. lol just experimenting with my girlfriends.
Just do what you want. keep it light. it's always better to look natural.