Mentally, probably mid or late 20s. Physically, I have no idea. I mean, I look older in the face but I dunno how you would measure a woman's body. I have a female chest and all that jazz.
When I was a freshman in high school, people thought I was a senior. In sophomore year, someone confused me for a teacher. Last year, an employee thought I was my father's wife - which I took the most offense to, considering my father is in his 50s.
I take it as a compliment when people think I look a few years older and more mature than my true age. In the next 10 years, I will want to hear the exact opposite.