Lots of philosophy ages badly too.

Or, in other words, becomes science.

Philosophy is full of demonstrably false ideas where science has caught up and been able to test and find the truth of something, especially in the areas of philosophy of mind.

Even philosophy can age badly, so I'm not sure that holds. But I think of Jaynes's book as if not science, at least science-adjacent. It's definitely on the wild, fuzzy, not-even-proper-hypotheses end of the scale. Maybe we can compromise on the old term "natural philosophy".

Which is fine, honestly. Somebody else here compared him with Freud. Exploratory thinking about the natural world can still be worth reading even if much of it later turns out to be incorrect.