Catherine Zeta-Jones and Michael Douglas’ secret for saving their foundering 24-year marriage?

Spending time apart! Catherine, 54, and Michael, 79, admit their May-December relationship has had its share of ups and downs. The Fatal Attraction stud’s battled alcoholism, tongue cancer and talk he was a sex addict while Catherine’s been diagnosed with bipolar disorder.

The stars even split in 2013 but reconciled after therapy. With their kids, Dylan, 23, and Carys, 20, grown up, the couple found they were spending large chunks of time together with only each other to talk to — which was hindering their hopes of living happily ever after.

“Their children have always been their number one priority, but now that the kids are off on their own, they had to come up with a plan to keep from getting on each other’s nerves,” an insider exclusively tells In Touch.

“Catherine suggested they go their own ways more often, pursuing their individual hobbies and projects,” the source spills, especially since movie roles for both of them have dried up in recent years.

Michael has started mentoring young actors as well as students at his alma mater, the University of California at Santa Barbara. He’s also looking for a project to produce.

“Catherine is keeping busy with her hobbies — sewing and gardening, and she’s playing a lot of golf with friends,” the tipster explains. “They also agreed to stay away from heavy topics that might lead to arguments.”