The "decline after 60" conclusion of the article rings true to me. I switched intellectual focus and mastered entirely new fields regularly throughout the 40

The "decline after 60" conclusion of the article rings true to me. I switched intellectual focus and mastered entirely new fields regularly throughout the 40 years between when I left college at age 20, and my early 60s. That switching and new learning kept me fresh, and my ability to do productive intellectual work - the mental speed measured in the Nature article - held up very well. But it began to noticeably decline in my early 60s. This was not due to life choices, as you suggest - I had an active interest and incentives, and put effort into, maintaining my abilities, and probably had more time and opportunity than ever. Rather, it just became noticeably harder to learn, and to use learning to solve problems or do creative work. A data point of one proves nothing, of course. But my experience at the very least provides no counterexample to the article's hypothesis. As for the physical - sure, you can maintain a greater peak performance than what most people do, as you age. But regardless of the effort, it's pretty much going to go down hill - strength, reaction time, coordination - after you're 30. You can slow it down, maybe dramatically if you're on the tail of the curve and put enough effort in (c.f. Tom Brady), but you can't stop it. And the effort required per "retained ability" just goes up.