Chrome book/OS for 91 year old

I'd like to replace my father's window pc with something simpler. I'm thinking ChromeOS. He's likely to only use it as a desktop with an external keyboard, mouse, and monitor.

I'm not familiar with ChromeOS. What are the minimum specs I should look for? Is there anything out there with in a NUC form factor? Any suggestions? Can I install ChromeOS on my own hardware?