The Age Project is a rather interesting idea. It enlightens the guessers who are likely to get better and better at identifying age as well as the submitter, who finds out how old people secretly think they are. I guess you have to be prepared for an answer you don’t expect, or want though. The other problem is that submitters might be lying about their age and simply want to know how old other people think them.
It’s still a great idea though! You could even submit pictures of yourself in different clothes and see which looks youngest!