How old was Jax during the fall of Icathia?

The story where "Icathia Once Stood" references his childhood: 'Saijax was the beating heart of the Kohari, a shaven-headed giant with skin pockmarked by the ravages of a childhood illness, and a forked beard stiffened to points with wax and white chalk.' Although this doesn't help me out much, because we don't know WHEN the childhood was :/

We can deduce from what we know of the timeline that Jax is at least around 1000 years old, but we don't know when he was born, so this is a wild guess. And he doesn't seem to age for some reason, so for all we know he could be much older. Thoughts? Would be so great if a rioter commented :v