That's Japan! Once you don't look quite right in a sailor suit, you're on the road to Old Maidsville. I don't get it either. Hot-ass AIKA started doing videos for Madonna about two years ago! I don't know her real age but to my western mind, she is not someone I would describe as an "older woman". Cultural differences.
No way is she old, unless the "married women" role's age range has dropped significantly. If she had her shorter hair, I wouldn't question her one bit if she came up to me and told me she was a college student. But like you said, there might be some cultural differences at play here.
I can't help but feel that Ai's career path has taken a weird turn because of her decision to grow out her hair. If it really was fan driven, then shame on them. There aren't many JAV actress that can pull off the short hair look as well as Ai has, turning her into a mediocre long haired actress is just heart breaking and incredibly stupid if you ask me. It feels like once an actress steps into certain roles, they don't seem to go back (I have no statistics, so please correct me if I'm wrong).