Protagonist age question

i don't think so; you might want to weave in her lack of wisdom and experience as a character trait.

I wrote a story w/ a 20-year-old female character. She was experienced but not too experienced, if that makes any sense.

The market leans rather older than that for protagonists these days, but I don't think anything over the age of consent is an acxtual problem. Most of what I am picking up tends to have the heroine mid-20s to mid-30s but there are examples well outside that range.

Perhaps you are writing something that actually takes a 20 yr old woman through the experience of first love and first sensual feelings. That could be very interesting. Kind of like going from bud to full bloom.