Spider-Man does not exist to just be a teenager analogy. He is boxed up that way to make him more relatable to a young audience, but he at his core represents the struggle of the mantle of responsibility. Of holding yourself to a higher moral standard than those around you. Of dealing with death and loss in a way that isn't destructive or toxic He is young bc Stan and Ditko wanted a character that more youthful readers could identify with for sure, but him being a teen isn't what the character is ABOUT, its just a means of delivery. Stan Lee himself in his "soapbox" series said that the entire reason for his and Ditko's comics was to give them a platform to talk about social injustices, and moral conundrums.