What if she's really, really hot?
Captain, they are fake characters... LOL, they could be 30 years old and will look exactly the same in anime. It's just that they love the whole "school" environment. That's really what you're commenting on. Most of those things don't touch on an actual age. Everything is hypothetical, and presented based on culture. It's not a big deal. You need to relax. We have so much fucked up things happen in real life, you shouldn't worry about a drawing made by some random guy. It's like condemning people who like to have sex in school-girl role play outfits. You need to separate things. Stop getting offended by literally nothing.
My issue with a lot of Japanese creations in that medium is that they are designed poorly. Not only do they look dumb to the role, then they get the most annoying voices, and act like complete morons. I dislike it on a creativity standpoint. The end result of their work. But again, I preach no starting biased based on a form of art. And it is art.