A little disappointing that you do the young man's route and he has a micro penis I hope it's not definitive because I don't see much fun to do the father's route if it exists
I don't think it's bad either, but creating this "physical" difference in an +18 game where if you want something more intense you end up having to play only one route. I wouldn't see a problem if the son wasn't tiny just because he's younger than his father.
It gives the impression that the boy will only serve to be a "punching bag" while the father has all the fun.