You have every right to be concerned! He needs to realize that he's been given a "gift'and should listen to his doctor. Overdoing it too soon could cause the screws to fail, leading to another operation and a longer recuperation. Good luck to your mom in keeping him "in line"!
My step-dad rarely listens to anyone. I'm afraid he'll start feeling better and want to get back to work at the store.
Lord knows, he doesn't need the money. He just ~needs~ it.