>it's the job that keeps you fit

I'm not so sure. I think cause and effect might be otherwise - either you quit working when you go gaga, or both are a function of age. Certainly my relatives stayed sharp after retiring but often went a bit demented around 85-90.

There's evidence at least some dementia is related to infections which may be easier to fix than other things. (as in https://www.theguardian.com/lifeandstyle/2024/dec/01/the-bra...)