...some of my favorite characters are very often the ones least like me.

Totally! For instance, my absolute favorite on BSG is Starbuck, who's pretty brash and arrogant, and a bit mentally unstable... but is she ever awesome.

I'm basically promoting ageism to prevent sexism...

Ehh... is it really ageist to say that teen girls are somewhat less mature? It *is* the truth, but fortunately for them, they will grow out of it with actual life experience!