> Mental atrophy due to less learning/thinking, isolation, loss of meaning and purpose happens first.

Except early onset Alzheimers happens and it also happens to plenty of people for which none of those are true.

Exactly. My mom lost her job because of early onset. She was very social, read tons of books, etc…. Now, I’m happy she at least still knows who am, but she can’t put a sentence together.

Example: Claude Shannon