EDIT: I agree though that the parental response that you described is extremely unrealistic if that’s how it was portrayed. I haven’t seen the movie and never will.
It makes sense in context. The two are good friends well before it gets sexual. The dad knows and likes the older guy well enough to invite him to their house for the summer so it’s not like he’s some rando old dude. And there’s no “preying,” it’s entirely consensual.
17 and 24 isn’t a big deal. I don’t see how that would appeal to pedophiles since pedophiles are known to prey on children, not young men that are legally adults in most states and countries.
In the novel they are 17 and 24. I don’t remember that being mentioned in the film, where they look 14 and 40.
It’s not mentioned but there’s no reason to doubt it. Elio is almost out of high school. Oliver is in college. It’s not supposed to be weird. Like I said Hammer is 31 and Chalamet is 22. You can criticize the casting but the movie isn’t about pedophilia.