Going back to the age discussion for a bit.
Everyone in KH2 thinks Sora is Roxas, at the time the explanation was Nobody Stuff, but nowadays we know about Ven. I wonder if Ventus heart started to awake in Sora during KH1 after he picked the Keyblade and started to affect Sora's body, and that's why by KH2 Sora goes through such a drastic change, not only in height but also his hair color changing and even his face model.
Would also explain why Roxas doesn't change at all between his birth in Twilight Town when Sora was supposed to be 14, yet Rox looked identical to the 16 year old Ven and did not change during the 1 year time period he was alive (even if physically his body was around 17?)
Meanwhile, Naminé DOES seem to age a bit inbetween games. Could just be an artstyle change, obviously, but her KH2 appearance looks slightly more mature than her CoM. This doesn't really reflect on Re:CoM however as they obviously just reused models to cut time.
The Original Org members, who knows lol We could justify that Lea and Isa had a growth spurt for the 1~3? years they worked as apprentices before things went south, but in Ienzo's case nothing else really justifies what he went through (although KH3 Ienzo does look a bit older than CoM Zexion, at least to me) other than actually growing up while he was a Nobody.
In the end the true reason is that in KH adult characters are design-coded as "tall" while teens are "medium" and kids are "short", lmao