I think the reason why people view relationships between young people and older people negatively is that psychologically, young people are not mature enough to deal with certain decisions or circumstances and are in fact prone to manipulation. I don't usually like these kinds of stories because they tend to romanticise these types of relationships or situations, which are delicate (I don't know if this is the case as I haven't read the book), but I have come across many that do.
On the other hand, I don't find it strange that the author knows many songs from the 80s. In fact, in my opinion, the best music was made in that decade, and I say this because I know a very long repertoire of songs from the 50s, and I'm only thirty years old, lol.
I really liked your post
RE: Book Review: "Kat and Mister Hartford," by Sara Hart O'Brie