-Us , Him and her
Have you checked your state and national park websites? Depending on your area, there will be trail maps for hiking, water-oriented parks for boating and swimming, and possibly an activity schedule for park cleanups and other group activities. The public nature parks of the US are among the best in the world.
Something as simple as a regular walk after dinner or a Sunday afternoon hike can be very rewarding. Lawn games can also be easy and lifelong interest. Simply playing outdoors in the evening are my best memories of childhood.
If you have been active without children you may find that life slows down a great deal for about a decade and a half. Maybe your cravings for activity can also be met through private time with your partner.