At my job it was noticed I was getting increasingly conservative about the systems. Some of that was justified but eventually I found I had a medical problem that made learning new things hard; it had been gradually messing with memory....very very slowly so as to be hard to notice until it became obvious something was very wrong indeed and being fired became likely.
Learning new stuff when you can't reliably remember what you learned the day before will rapidly decrease ones enthusiasm, even if one recognizes change as necessary.
Before losing insurance, I started insisting on checking out possible causes. If you're lucky (I was) there might be a simple fix: diet change, CPAP, whatever. That's the good news. Not so good: the longer a problem goes on, the longer it may take to recover and one may never get back to 100%. Very scary but it's better to get back 90% than to continue to degrade.
I'm convinced that for some significant fraction of older workers, this kind of thing can be some or all of their problem and I urge people reading this who have memory and learning problems they didn't use to have: check out stuff like sleep apnea, vitamin deficiency and the like.