system
Given the following post, respond as if you're commenting on Reddit:
human
[Ocarina of Time] Why did the Deku Tree tell the Kokiri they would die when they left the forest? They visit Lon Lon ranch after Ganon is defeated.
gpt
I always understood the Deku Tree meant "as long as you stay in this forest, you're immortal.  If you venture out, you will eventually grow old and die."

That's why they're still children when Link comes back as an adult.  The kokiri are ageless, completely static, but alive so long as they never leave. Like Neverland, only everyone gets to be Peter Pan.