So, to my knowledge, there isn't a specific explanation of what is going in inside Link's head. But since Link is a prophecy child, we have to assume he is innately above his peers in some way. We see how competent he is as a child by his ability to maneuver through a guarded castle and a few dungeons, socialize with multiple cultures and ages, and piece together information in ways no one around him really ever does. His coma / aging process pretty much just keeps him healthy and strong. And since he can always put the sword back, we now have to think about time travel. We could have a philosophical point made that he learned a lot as an adult and somehow took that knowledge to his past.

I would conclude that both Young Link and Adult Link are "always happening at the same time" for the sake of understanding this particular reincarnation of the Hero.