Do you think Bitcoin Core is too complicated?
I don't know your particular case, but it's probably the most secure, which he would likely appreciate. He might also be interested in contributing to the network by running a full node if he has the networking requirements and his setup is up to it. Even if his storage can't hold the whole blockchain you could prune it down to fit.
It's also pretty easy to use in my opinion.
One's never too old to learn something new anyways. Unless one says they are I guess.
Whatever you decide, good luck.
Onboarding can be a tricky business.