It's typically US-centric to assume the age of consent is 18 everywhere in the world (here in the UK, it is 16). Anyway, Call Me By Your Name is a brilliantly acted and directed film.
On the subject of age gaps, I am getting increasingly pissed off with sanctimonious condescending nitwits who think they have the right to dictate morality to everyone else. There are really only two questions: 1) Are both parties over the age of consent?, and 2) Are both parties consenting? If the answer to both questions is yes, it is none of anyone else's bloody business.