I can see 12-15...I myself am 16, and like Thelis said the way you dress affects how old you look...
...Also maybe the fact that in your picture you look small and not quite 5'9..more like 5'5 or 5'6. I took a photojournalism class and we studied that...a picture that shows more of you and less of the background would help.
Not to make this a work-out thread, but if you put on a few pounds (and I don't mean 20) and just start working out the right way to gain SIZE, you'll see results. People can work out all their life and they'll just be really cut, but they wont gain size.
Honestly I'd recommend not even worrying about getting buff yet; your body is still growing and you don't want to make the mistake that many young weight trainers do.
i think you look young, but i dont think you look 12, thats a bit extreme, im 16 6'1" and people who dont know me at school then meet me think im a junior which i am a sophomore