I too was expecting a minor child, not a young-ish adult.

I don't feel like checking it now but Linus was pretty young too when he released his kernel.

Yep; Linus Torvalds born 1969 would have been ~22 years old when Linux was first released in 1991. -- https://en.wikipedia.org/wiki/Linux & https://en.wikipedia.org/wiki/Linus_Torvalds

You could do something like this at 15. I worked some on my own little hobby OS when I was 17 (maybe a little younger though bit hazy on that). I learned what I wanted to out of it though and it never got this far.

Fair enough, but given the quality and maturity of his writing, I was expecting some kind of middle-aged wise man.