This article and post is timely, because I "retired" last Friday (I'm 37). It doesn't ring true at all to me that retiring would necessarily be bad for your cognitive skills. Maybe it depends on the type of person, but I'm engrossed in personal cognitive pursuits, such as teaching myself machine learning, putting together an app of my own for the first time, indulging my writing hobby, and of course spending more time with my daughter. It is these very pursuits which led to me retiring; I want to throw myself completely into them instead of dabbling with them on the side. I don't see how someone would "lose their mind" from retiring, unless retiring aggravated other vices such as drinking or watching excessive television.

I've no doubt one's personality slowly changes when no longer chained to authorities saying what to do and when to do it, and when no longer exposed to corporate "culture". That's quite different than one's brain turning to goop. After only a week, my brain feels clearer than ever as the cobwebs of work stress slowly clear away (it still hasn't landed that I don't have to work ever again). Maybe his friends who are "losing their minds" are just seeing the world a bit more clearly? Or perhaps they were uniquely unsuited to retirement, lacking any intellectual pursuits?

I'll probably write an article on my experience in a year or two and let you know if my brain has turned to goop, assuming I can still read/write when that time comes!

Edit: as long as we’re throwing out competing anecdotes, the only person I know personally who retired so early is wildly successful. Far more than he was at work.