Not a western country, I take it? It sounds like your country is pretty strict and conservative when it comes to sex. And to expand on this point;I don't know what country you live in, but where I come from a lot of girls won't even blow their boyfriends.
I think it's dishonest too look at ORS through this point of view, since they're western people, in a western country. It's not uncommon in these countries for young people to talk openly about what they're into or not in bed, even with people they don't know all that well, in casual conversations. The level of how much they share/how crudely they talk about it varies from each country.You must be registered to see the links
So yeah by eastern standards, an average person with an active sex life in their 20s is a sexual demon, going by their preferences and amount of sexual experience they have.
This logic just doesn't apply to ORS though because none of the characters in the game come from a radically different culture with strict views on sex and relationships.