I am becoming increasingly convinced by a crack theory of mine that Ye Zun makes the Hallows sometime in the future, sends them back in time/they send themselves back in time, and so they imprisoned him for 10K years to keep him safe and ~~Preserve The Timeline~~. This also explains why there's no user manual and their fixation on ZYL.
Honestly, that makes as much sense as anything. It handily explains all the things!

With sufficiently large numbers like that (such as Methos being 5000 years old in Highlander), I assume a lot of wiggle room on either side, like several hundred years could go by while the war was still "ten thousand years ago".
Oh, yes, but I wanted to highlight Zhang Shi bringing up his age at the specificity of the hundreds, rather than the thousands of years. More accuracy!