Comment by Aurornis

Most of the 40+ intellectually driven people I know have family and kids.

Honestly, having kids seems to focus people and help them drive toward efficiency and priorities.

I think some people just slow down more than others when they age.

Alternatively, their priorities might simply be revealed by their preferences and energy allocation. Like the people who want to be very physically fit, but when it’s time to work out they can’t find the motivation.

Speaking of fitness, 40s is when lifestyle and health choices start to catch up to people. The cumulative impact of diet, sleep, exercise, and choices like alcohol consumption start to appear in the 40s or even 30s. There was a stark split among my friends in the 30s where those of us who stayed fit and had even moderately healthy diet, sleep, and lifestyle diverged from those who ate whatever they wanted, didn’t exercise, or even frequently drank alcohol. Claiming a lack of energy due to age (or blaming family, career, kids, etc) was the first major divergence.