Age gaps can be very creepy. For example, I’m not sure why someone would wanna date someone they legally can’t drink with, or go to some adult spaces with, even if they are a legal adult. Someone else on here explains it well so i wont get into too much depth on the creepiness of age gap relationships, so I’ll say what i’m personally okay with.
I only accept a maximum 9 year age gap if both characters are above 21, and that age gap can increase as the younger party is older. For example, a 30 year old with someone who’s 45+ is less weird than a 20 year old with someone 35+. Even weirder when you see those types of relationships in fiction mimic an adult-child dynamic. But that’s largely the appeal of those types of relationships. Personally, I’ll DNF a story with those kinds of age gaps.