I can completely understand how your DH feels! Some of my predecessors worked until an older age then myself, but what triggered retirement in most cases was change. Change of location, change of supervisors and upper management repeating the same mistakes over and over because they weren't around when their solution had previously been tested and failed.
Fortunately for me I reached retirement before I felt completely disheartened but I have friends still working that can't wait to get out and of course there is a line up for people who actually want these jobs because the salary and benefits are excellent. There is an old saying about history repeating itself, and I just saw it happen too many times. It's like no one takes note of mistakes or seems to remember failure. Now, there were also plenty of successes to celebrate as well, not to be a complete Debbie downer, but, I was middle management and got to teach my supervisor too many times. I must make note that I had opportunities to move up that after I got to a certain age I wasn't so keen on because I had a lot of freedom to make decisions at my level, and I was happy after 4 or 5 promotions. Maybe if I had started younger I would have felt differently motivated. I think I left when I still had a lot of earned respect, if you know what I mean. The psyche needs to feel appreciated and I can say I definitely did.
I did have to alter my thinking in my last year and learn to support in different ways. Sometimes its not clear to the person that has to accept decisions made above you why the decisions had to be made, and were essential because dynamics themselves have changed. That said, I know I left pretty much fully intact and without regrets and didn't have to leave to look for supplemental employment as happens when burnout comes before you are in a good spot to retire. And, I am not a FIRE personality because I needed to be a worker in the years I worked. Now I can enjoy relaxing, but not in my forties or earlier.