Can't ages be changed anymore??
You can manually change them by modifying the script, or using URM, but dev has gone quite far to eliminate the possibility of underage characters. The game now makes many mentions throughout about the girls all being adults, in university, all having graduated high school, etc. At this point, even a fan-made age patch to restore such content would be a pretty major endeavor, which would require a new version with each update.
It would also require modifying the same files as the ipatch, which would cause compatibility issues, unless
MountainMonster66 were willing to incorporate it. At this point, it's probably best just to consider this a game about becoming a teacher at a university for very young-looking adults.