I'm 22 and people think I look 16-18.
Funny thing though... I don't smoke, but I did buy my Dad a pack of smokes and the lady at the store just looked at me. I then told her I need a pack, and then she goes "ID" like she didn't think I had any. I got my wallet out and showed her my ID. She then looked at me again and goes "Take it out, I don't know if its fake or not." This really made me mad, and she knew it. I did get the smokes though. I was so close to just giving her the pack back and saying I don't know if there fake or not, and then walking out... oh well...