Wow, that one is even worse, pure ageism. He might as well write about "when to hire female people" etc. Somewhat sad that "culture" is mostly a meaningless buzzword these days, used mainly to exclude people you don't like.
"When to hire 'old people'?" <-- is a ridiculous question.
"Should you take asshat advice?" <-- see Betteridge's Law.
Edit: Depersonalized the target of "asshat" because I'm not in a position to judge the person, just this particular post.
If you read the book, there were only a few fairly badly communicated or stupid parts, and they made a lot more sense in context (it is partially biographical, so he includes mistakes and why they were mistakes).
The "old people" is one of those which made more sense in context. It was a bad idea to let it be pulled out like this, imo.