Worked at a startup with about 20 or so people. The cofounders decided to bring on a "COO" to, in essence, whip the company into shape for scaling. This person was considerably older than a lot of the staff (but I'm not sure age was relevant).

The person was a terrible cultural fit and was the reason three of our best employees left, dynamically changing the structure of the co. I think this person made some decent operational changes, but the culture value that was lost didn't make up for it.

(don't really have much followup to where they're at now, left a while back and haven't heard much from former coworkers).