I don't think you should care much about it. Since the character are characters and not real people on a screen.
That is a fiction after all.
Only that people under age shouldn't play those games. (Without parents permission!) and that game aren't even porn since the original had only two sex scenes per route and not all routes had those two those just showing a piece of life.
Add the characters are not even humans.
Maybe if that showed a real teenager 13 years old having sex with a 40 years old real person in a photo or video. But I do remember some king centuries ago married with a 13 woman somewhere in Europe.