Yeah, you can pass it off initially when the MC is unsure about what she wants to do with the old man. It's all part of the journey, deciding just what her kinks are. Eventually though she realises that she likes having sex with older guys and the madame helps her realise that, and tells Jane that it's one of her kinks too and that it's perfectly ok for her to have sex with a guy old enough to be her grandfather, if she so wishes.
This is obviously a central theme of the game, which you don't seem to have realised. All games have specific themes which you have no choice but to follow, once you've made the decision to play and this is no different. I reckon if the MC was only into younger guys, and went nowhere near older men, we wouldn't be having this discussion, because you'd be perfectly ok with that. There is absolutely no difference between that and what we have in this game, except that it doesn't coincide with your personal preferences.
For me, I would have thought to myself at that point, do I really want to keep playing a game that has unavoidable content that I don't like. And if the answer was no I don't like this content, I would have cut my losses and stopped playing and moved on to one of the hundreds of other games on this site, with content that I do like. Literally everyday at least 2/3 games that I follow are updated and it's impossible to keep up to date with all of them. It's not like you don't have options that forces you to keep torturing yourself by sticking with a game that you don't like.
This is what I don't understand, because it's self evident to me, that there are going to be games that I start, but subsequently decide I don't like, so I stop playing them. It's just a fact of life, that some things just don't fit to my preferences and constantly moaning about them is counter-productive, and unlikely to bring me any joy