I’d argue that sticking Peter perpetually in high school is still not coming of age. That’s just an animated sitcom like The Simpsons. Or classic Archie (and even Archie has grown up and even died).
Coming of age is about firsts - as firsts are usually integral to loss of innocence. First kiss, first falling in love, first break up, first real experience with death, first loss of someone important, first real adult responsibility, first job, first time having sex, etc.
The thing about firsts is that there are only one. Once the first is over…it’s over. And can’t be repeated or recovered.
That’s why stories set in high school inevitably move beyond high school if they want to have any verisimilitude and real life resonance. Or they remain sitcoms where the situation is what matters, not the characters who are just archetypes/stereotypes.
It’s so funny - both haha and head scratching - that Spider-Man has his premier place in the pantheon of pop culture heroes BECAUSE he was allowed to have his firsts, learn from them, and grow. The classic stories everyone points to are all about Peter learning from and being affected by his experiences: AF 15, Death of Gwen Stacy, KLH, The Conversation, The Child Within/Death of Harry Osborn, If This Be My Destiny, even the Clone Saga - and yet there is this school of thought that this has harmed the character and therefore should never be allowed to occur moving forward?! It’s so unfathomable to me. And it’s led to the character completely spinning his wheels and an ever increasing tendency to just homage classic stories with ever diminishing results and ever more audience ennui. No wonder USM is outperforming - it allows its Peter Parker to be a person first, not a two dimensional cartoon mascot like current 616.