I could tell similar stories about other family members and people I know. My brother is perpetually about 8. My mom has always been about 40, that I can remember -- when she was little she used to be protective of her younger sister, and even followed her to the principal's office once when her sister got in trouble for something; and my entire life, she's periodically had these mid-life-crisis like periods and needed to reinvent herself, which I think is also stereotypically ~40 behavior. My childhood friend Lucie I would probably put at about 22. I saw her a few years ago when my sister got married -- she was visiting Plymouth from I guess Virginia -- and she was still the same. She had a new tattoo and still wore nice artfully applied makeup, but hadn't really found a career yet. Someone I met in Florida, Mike, is self-employed selling martial arts weapons on the Internet, and he says he has always found making a living and taking care of responsibilities easy -- started working when he was 15. I would guess that even then, he acted his age of 35-ish.
Me, I think I'm always going to be about 16.