I know people who have raised multiple kids beyond the point of them graduating from college and themselves starting their own families who are still in this industry (by choice), and are still sharp as ever.

I've also worked with people who are 25 years old and who have clearly given up on life or anything more than turning the crank and getting their biweekly ration of pellets. They live in fear of being discovered or "found out" and turned out on the street to sell the Mercury News on the onramp to 101.

Age, experience, rigor, knowledge, energy level, mindset. Don't confuse one for any of the others. It's a multi-dimensional problem. Also, it isn't static.

I can probably give you an example of a coworker at any position in that n-way space just from my own experiences, and that's only with a 25 year career. I can only imagine what else I'll encounter next.