Um, I'm 18, a senior in HS, and have been an Alto since I was in 8th grade.
Quickly - Freshman and Sophomore year, I was in "Women's Chorus," and sang Alto. Clearly, this was an all girls choir.
Junior year I auditioned for, and was accepted into "Vocal Ensemble," the top choir at my school. That year I was one of 6 altos, but the only junior alto.
This year I am Alto II section leader, by default. Oh, and I'm now one of 8 altos, but one of 4 second altos.