A long eye relief scpoe would cetainly help, but maybe
that gun no longer fits him properly either.
As you get older you tend to hunch forward more because of muscle and bone loss..
So maybe now the stock is too short, and no longer recoiling straight back onto his shoulder,with muscle and bone loss, he is too week to handle the recoil going up.
If he loves his gun and you know you are not going to convince him to change the stock design maybe a recoil thicker reducer pad added to the end of the butt may keep a little more distance betwen thescpoe and his forhead.
If you can convince him,change the mounts they are probably wrong for him as well....