As others have said, 40 demographically is no longer a sign of serious middle age. Fifty is well established as the new forty. Probably for you, mid nineties would be your life expectancy based on the "normal distribution curve". For instance, I'm 65 and the average for me is another 19 years. How do we live our full lives and stay healthy ? Exercise our cardiac system every day, consume a healthy diet, avoid things that will kill us and keep an active mind. People in their seventies, eighties and nineties at the sports centre where I worked did several exercise sessions a week such as tennis or indoor bowls, and showed no signs of keeling over. One man 92 was on his third Russian wife.
There is a change in our working lives. We reach a stage where we have progressed as far upwards as we are likely to go, and consolidate our position. This is not all bad because we can take a more relaxed attitude: the pressure is off and we can enjoy our work. Nowadays we are still climbing in our forties and beginning to consolidate by our mid fifties. We are expected to work longer, though, but you could go for a later life career change to an easier job particularly if you have been paying into pensions etc.
The third age is really great ! This is because everyone who follows these forums are the sort of people who will use some of their time for discovery and education - we never stop learning. I've learned so much in the past seven months about subjects that interest me. There is also the opportunity to put something back into society.
So don't worry that he years pass. There is a lot to look forward to if you make the most of each situation. Try to sort out your health problems as soon as you can, though. Good luck and remember that we're always here to chat about your feelings.