I worked at a desk job till I was 64. Even at that age, I found my faculties were waning regarding problem solving, later in the day. If a knotty issue arose, I knew I'd need to attend to it in the morning rather than the afternoon, when I dealt with more mundane issues.
So even with a desk job, as we age, we become more fatigued and the longer we are forced to work, the more evident that will become.
I think there's a real problem for people who work in physically demanding jobs. Imo, they are most likely to need to retire earlier, or face serious ill health.