i have that problem. i'm 18 and i still sometimes get ID'd to check that i'm over 16. and last year someone told me that he had thought i was about 12 (it was a guy i worked with who later started hitting on me. which was worrying). whether or not you can do stuff depends on how you look. some girls can look older just by wearing make-up but other people just have young-looking faces (round face, large eyes etc. plus if you're short people assume things). look on the bright side, you can probably still get child bus-fares and when you are older, people will still be saying you look young - and, by then, it'll be a good thing!