Pyenv! Let the OS have its own version and work on whatever version you want, whenever.

Probably an unpopular opinion on here, but the OS I recommend for grandparents and parents is ChromeOS. It’s so locked down that it’s almost indestructible, and they almost never need any specialized software that you’d use Windows/MacOS for. If you’re savvy enough you can also use Linux on it in a container, which is how I prefer to use it for day to day stuff (in my case, data related workflows).