I'm only 15, but I feel like I'm 27 or 30 or something.
Not by a landslide, but I'm more polite than most all of my friends, an extremely profound vocabulary, tons of literary, poetic, and historical knowledge, as well as a ♥♥♥♥-ton of musical info that most 15yo wouldn't know.
I wear a tie and dress shirt to school almost every day (with an occasional vest or sweater vest)
Also, I really dig socioeconomics and astrophysics, which I guess isn't something every teen says.
So yeah, I feel mature!