Heh, I'm 18, and I look 14-ish. It confuses the hell out of my classmates in university, I suspect. At least my friend says I look 16, which is two steps closer but still two steps too far. Most of the guys I've met tend to look younger than their chronological age, which is a bit of a curse, but after being some years on T, they do tend to finally look like their age.
Haircuts and fashion/style definitely contribute to how people perceive you, especially age-wise, I'll definitely second that.
Forever young... the epitome of being a trans guy.