I don't deny that getting older has an impact but your statements above are applicable to anyone and probably more so to older developers. Reading over your story the main thing that stuck out with me is that you've had a it rough for the past few years and its obviously had an impact on the career.
What I would add is to focus on your health. I don't know what problems you have but if you can work on the diet, work on the fitness, get on some kind of weight training program. The better you feel, the more energy you have will make you more effective everywhere else.
I started a few days ago. It hasn't been a good week for medical issues but things are looking up.
I've been to the Emergency Room twice since Sunday. And I had a fever of 102 degrees just a few hours ago. But I'm feeling O.K. and I'm scheduled to go back in a few hours to nail down what's happening physically.
Due to recent changes in U.S. laws, I might be able to qualify for medical care now. If it works out, this will be a big help.
What I would add is to focus on your health. I don't know what problems you have but if you can work on the diet, work on the fitness, get on some kind of weight training program. The better you feel, the more energy you have will make you more effective everywhere else.