Whenever I see a young success story like this, I get even more curious about the parents, which should be a whole nother article imho.
Children are capable of absolutely amazing things when they are told "yes" and given respect and minimum guidance. Of course my example is not as mind-blowing as this, but my son built his own forge and has made beautiful knives and swords from found metal. Tons of research and sweat and persistence on his part, and not ours. And if we were interviewed about it, the soundbites would come out about the same: "Yup, he did it, we were a bit worried, but he was managing the risks and knew and followed the necessary rules, so ultimately we trusted him."
Like, that's just few questions that come to my mind in like 2 seconds, I'm sure a competent interviewer could think of more.
My input into this was computer access, permission to proceed, "no you can't put it there", (then after he set it up in an approved spot) "neighbor says you have to move it further away from his yard", and buying the fuel since he's not old enough. Then one day dropping my jaw when he walks in the house with a beautiful knife.
A basic sandcasting setup sounds like something your son would be absolutely stoked on.