
Ouch! I've never been asked if I had a mentsl disease, (well, not in seriousness, anyway), but I'm often mistaken for 13 or even 12. (Once, TEN!)
I help out at a junior high youth group sometimes, and one day I was helping out at a retreat as a small group leader. Well, I was almost a foot shorter than most of the girls, added to the fact that I look really young. Someone camE up to us and asked where our leader was, and I pipe up, "*I* am!!!" in my kinda high-pitched voice.
I have a friend, though, who's 14 and looks closer to 18. It freaks her out when college guys come and hit on her.