I def don't mean to start anything but wh…

I def don't mean to start anything but why would a 5 year age gap be considered nasty? I think as long as they've both at least hit 18 it should be fine. My parents are 7 and a half years apart and I know couples who are 10 or more years apart

Yeah but the context is important. Nancy is 17-18 (a legal adult) and Dustin is her brother’s 13 year old best friend. Also they didn’t meet in their twenties, Nancy has known Dustin since he was 9 and has had minimal interactions with him till now. Framing their relationship in a romantic way is just unnecessary.