Come to think of it, I really have no idea how that works. Assuming you don't get Alzheimer's or some similar disease, when do your mental faculties start to significantly decline, and how much?
when do your mental faculties start to significantly decline, and how much?
Faculties that feed into fluid intelligence decline a lot from around age 20. Faculties that feed into crystallized intelligence decline less, and the decline starts (on average) in one's 60s at the earliest. (Based on an old InquilineKea post here.)
Here's an interesting post about calculating the value of your free time and why it might not be as simple as some tend to think.