In Lee-Ditko's run, Peter Parker was framed as being older than his generation and being more of an adult than his classmates, and I always saw Peter as the kid who grew up fast and didn't have time to really enjoy his youth. That was how it came across in that original run. This was a guy who quite obviously hated his teenage years, hated high school, had no friends, lost his Uncle, and had to work a job to care for his Aunt.
The great thing I love about the Master Planner Saga, was the entire issues showing how isolated Peter was from his classmates...he goes to his first day in college while Aunt May is in hospital dying and he has to work as Spider-Man to find a cure, and the entire time he goes to class he's on autopilot completely unaware of being in class. It's really amazing how Ditko captured a realistic stasis of being in that mode where your mind is so occupied that your present is some invisible unreal thing. And of course there's the poignancy that snobs like Harry, Flash, and Gwen don't understand that at all, nor can they ever understand it.
So to me it never made sense to think of Peter as young because he never really had a real youth until he went to college.