How to have fun

To preface this, I'm asking for my coworker who I happen to be sitting next to right now. He's a complete workaholic (works 80-100 hours a week) and recently he's been trying to expand his social skills and so I've been inviting him out with me and my friends just to hang out and get him out of work mode.

The thing he really struggles with is he doesn't know how to have fun. He told me he doesn't have any hobbies, doesn't really do much when he's not working except sleeping and watching TV/movies on occasion. I asked him if there's anything he's interested in trying out or learning, but he doesn't even know where to even start.

Anyone else have this issue and/or have any advice on this?