Unless you're jumping in the deep end and wanting a full hardline build, watercooling isn't as hard as it first appears. Let's be honest it's more plumbing than fancy tech. The only really scary thing is putting a block on the graphics card as that requires dismantling, but even then just take things slowly and follow the instructions to the letter.
To that end there's no reason why your nephew can't break his WC virginity. There are a bazillion references and guides across the intarwebz on how to do things, how to leak test, how to assemble, how to fill and drain, and of course plenty of experts here to bounce questions and opinions off. It's just a matter of confidence for your nephew.
And let's be honest, putting an AIO on a graphics card is identical in operation to putting a full block, so the only difference between AIO and full loop is the AIO is incredibly unlikely to leak, rather than very unlikely to leak.
See if you can talk him into it.
