i will sperg out in this post, sorry
I love the retcon that classic Sonic characters are children for aesthetic reasons, even if it's a weird soft retcon where they are somehow not any specific younger age than they were.
It's still really janky though and has the adverse effect of retroactively making the classic titles games where Sonic is a "child" (Even though he's apparently still a teenager, but is physically less mature or something?) There is an appeal to Sonic being this free roaming teenager who goes on adventures. Sonic being a tween or a child in the Sonic CD intro is conceptually silly.
The opposite interpretation, where Sonic is the same age and just sprouted taller and developed irises while being 15? Also silly.
And then there's the fact that it's clearly not treated as an actual in-universe biological growth. Cream and Marine are clearly not "classic" despite being younger than Classic Sonic must be.
Charmy has a classic form despite being a six year old.
Classic cannot be tied to a specific age group at all, because characters 6 and older have irises, and Classic Sonic can't be 5 years old... because modern Tails is 8, which would mean Tails wouldn't be born for another 2 years after the classic era for this whole idea to function as a strict world building rule.
Silly silly silly.