the title pretty much says it all but a game where the age of the girls is optional could work wonders, preferably with some incest but its not necessary
Long Lost Daughter has this feature, which works in a rather roundabout way. Near the beginning, it lets you choose the ages for the first year and final year students at the school you teach at... and those ages end up being used for most of the young girls in the game... including your twin daughters (the former) and the girls you teach (the latter), which includes the titular character.
I'd love to find more games that allow this, but I've played all these and most aren't allowed here. Dumb Koala's The Intern lets you choose the age of the titular intern.
Thanks, didn't know about that mod, definitely will make me enjoy that one even more. Of course, there's also Parental Love, with the patch, but who hasn't played that?
Honestly listing them all out like this makes me depressed to realize how few there are. This is one of my biggest fetishes and I wish there were more games that offered this, but I understand why they're rare.