I'm not sure if his age was ever made clear. I think there is a spin-off about him, but I'm not so sure as to how it relates to the main narrative.

How old is Han Tzu, aka "Hot Soup", in Ender's Game?
-
<sub>Inspired by this question: https://scifi.stackexchange.com/questions/114983/how-old-is-finn.</sub>