I like to think that if Kyuubi heals Naruto unconsciously, that he might even slow down the aging process. This is just really exaggerated. Like if Naruto was Wolverine. Grr!

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Aging

It hadn't been noticed when he first came home because things got hectic. There were invasions of villages, missions to complete, people to piss off, and crazy teammates to find and beat the shit out of. No one really noticed that Naruto hadn't changed at all.

Sasuke was the first to notice when he came back to the village. The only difference between the Naruto he had left for dead when they were twelve and the Naruto before him now was height.

"I don't age," Naruto explained. "Kyuubi won't let me."

While everyone else grew up, Naruto still looked fifteen.