Zoah is actually Crono, trying to conceal his identity by using a helmet and a voice-changer.
At 28 he's too young to be Crono though (I swear if somone says "Time Travel Game" I'm gonna!!!)
He, uh, was lying about his age so that Marle wouldn't find him and drag him back to their hut outside the ruins of Guardia castle to help look after their ten squalling brats! No time travel required, honest!
...gonna?
Shoot, now you've tempted me.
But I won't.
What about...
Crono traveled through time so much it screwed everything up and everyone and everything is actually Crono and eventually Crono becomes God? EXCEPT he already was God sending himself on a mission to save his beloved Entity? This would mean Magus=Crono: Zoah=Crono: Marle=Crono( ): Serge=Crono etc etc etc.
Tree #41 in the Guardia Forest=Crono. Entity=Crono!
Wouldn't that make every marriage in the Chronoverse incestuous? Not to mention that, when Magus found out he was actually Crono, he would fly into a rage and kill Crono, with the likely end result that everyone and everything in the universe would then be Magus? Which would mean that Schala was Magus, and the poor bastard just wasted years of his life looking for himself...