Yeah, its tricky. Especially with Marvel, where they've more or less had the same unbroken continuity since 1962 (arguably since 1939).
But time has inevitably passed in the Marvel Universe, even if its a fraction of how much has passed in the real world. And if we acknowledge that time is passing, then we should we okay with the characters ageing and progressing in their lives. And since its a shared universe, that has to apply to everyone.
There used to be a 4:1 ratio when it came to calculating 'Marvel Time'. Based on that its been over 15 years since Peter got bitten by the spider, making him 30ish. And I think that lines up well with the sheer volume of events that have happened in his life. While Peter's still young, I don't see the need for him to not have the life of a 30 year old, and instead try to act like a college kid.