By the way, don't let him know I called him "elderly"!
My first thought is to go ahead and recommend minimalist shoes just like we would anyone else, but I also asked the Sock Doc just to see if he had a different thought. Nope, he agreed. So, Have him check out the brands: Vivobarefoot (very minimalist and you feel everything) Skora (if they are back up and running these are good) Lems (a bit softer sole) Xero Shoes This assumes he's in good enough physical condition with the green light from his doctor to participate in the fitness program (which it sounds like he is)! You can always have a PT (or someone similar) look over his gait just to make sure he's moving well and no glaring issues with over-pronation, etc.
Thanks for confirming my thoughts. And yes, all activities are under PT and medical guidance. We have a NRC certified store locally here in Cleveland which I support and which we will be visiting. All the brands you mention are constants in my closet, with the addition of Topo Athletic.
Cool! Good luck and LMK how he likes them.