I showed interest at around this age and my dad showed me CentOS and building basic webpages. I didn’t take too much interest in that, but I asked him if we could build a Counter Strike server and he obliged. He’s a nerd himself so we had a static IP for the server and everything. Worked well!

Anyway, I would recommend getting an old desktop and installing Ubuntu server or desktop edition with a desktop environment. Show him how to navigate the command line and what that means if you follow the file explorer at the same time. And then hosting very basic things(webpages, local game servers, etc.).

He might really latch onto it, or might not be interested whatsoever. I latched onto it, ended up building my own PCs soon after, and have my own homelab and I work as a full time Linux sysadmin now.