@PokeyJoe has a very interesting idea, but first I would ask your son to sit down with you one time when you pay the bills. And show him one of your pay stubs, too.
Young people often don’t realize how much of a person’s gross salary goes toward boring stuff like taxes, health insurance, utilities, groceries, phone and cable bills, car repairs, and medical stuff. It can be shocking to see that thousands of dollars a month go to these things – before any money is spent on anything that’s fun or interesting.