Does it explain this later in the game or did i miss something? I am barely on the quasimoto level by the way.

Erm... they explain it right away

"Yen Sid's magic"

Cause they enter the dream realm

Yeah, you missed it(dont know how).

i understand how. I am asking why. is there some kind of significant meaning to their ages changing?

Does it explain this later in the game or did i miss something? I am barely on the quasimoto level by the way.

 

the changed clothes will be explained at the end of the game

but the age....I don't know

Yen Sid's magic. he wanted them to forget all they learned with the Keybllade to start fresh, so he changed their appearances so they could really get deep with this change (that's what I understood)

DDD is set in the Sleeping Worlds, these worlds are in slumber and therefore aren't affected by the future. It is set in the past. Thats why Sora and Riku look lik their KH1 selfs.

Thanks guys who actually understood the question.

They returned to before their world was swallowed by darkness, backi when they looked that way.