Friend, I'm in my 50s now and I can tell you that you really are only just getting started. I highly recommend finding a new activity or social group and without making massive changes, as those can feel daunting, just make a small change to involve yourself with that. Even just once a month being part of a park run club, or getting to know people in your local art scene, or doing a cooking course, can start you down a path that will enrich your life.