@mapleleaf: in the real world. You don't really think that my behaviour on webdip tells you anything about my behaviour in life, do you? You're probably trolling, but just saying.
@Octavious: Actually, children say it too.
It sort of depends on how old I want to be guessed too, I'm a good actor. Acting young is pretty easy especially since I'm young and acting old is a skill I learned, so...
I just look older because of facial hair for example, and my behaviour is pretty grown-up too: assertive, calm and some other things that I don't dare to say because I'm biased. I also have a distinctive walk (read: you can see that something happened that affected my walk) and other stuff that tells you some of my experiences. I suppose looking experienced makes you look older too, because, well, if you're older you have more experience in general.
But yeah, it really depends on the situation.