[Insanity]

It probably is. But, given a reason as "not being a good cultural fit" does not have to describe that it is about age I presume.

I guess that you can always make up some kind of excuse other than just saying "too old". But I am unaware of how they corresponded this to the person in question.

[basseq]

It's hard to understand whether this was a concern backed by data (observation), or general discrimination.

The former is legitimate: "this person will have issues with management and cause problems". The reason for this is a moot point: the candidate has issues with younger people, the candidate has a chip on his or her shoulder, or some other reason.

The latter is questionable: "This person is old, and old people have issues working for younger people, so we won't hire him."