Senior in high school at 16?
FWIW, I'll be done with undergrad work at college at 21 (assuming I graduate on time next year). Could have finished by this summer (ie: before I turned 21), but, I do enough classwork during the semester, I wanted my summers "off" (read; working/internships instead of classes).
FWIW, I don't recommend this, but (and I've faced this with my own kids now) there's really not much choice. I was already bored in school; if I'd been back another year, it would've been even worse.