just have him get away from these rocket launchers they call fly rods these days and get him into a nice older (or new) glass or bamboo rod. They literally cast themselves. And, as mentioned, technique. While I don't ever have joint pain after a day of fishing, I do notice that I'm a bit more tired when I throw the 7wt fast graphite cannon vs. when I throw my nice and easy casting Fenwick FF857. besides, it'll throw just as much line anyway...and easier. Even in the wind, it just requires so little effort to cast.
"Some people fish their entire lives without realizing it's not the fish they're after."