Also middle aged and in a similar position. What helped me was doing something creative. Not exercise. Writing and working outdoors. I find losing myself in an activity really soothing. It doesn't change the facts in my life but it does help me feel less depressed. It's that being in the moment thing. When you're just concentrating on planting or digging or something outside yourself. I still have all the limitations and things I need to do, but I feel less bad about them.