These people don't have to be very old at all, actually. I've seen plenty of young people start acting like this at a company after working there only a year or two.

That being said, if it is an older person doing this, then it can be difficult to let them go without it appearing to be due to age discrimination.

But I've seen enough layoffs to know that for a lot of companies, it's all about saving money by getting rid of these people, not about their performance, at least every time I've seen it happen.

I've even been told directly in a layoff it was because I was one of the higher paid people in the company (it was a game studio, so I still wasn't being paid all that much). I guess I was old for someone in the game industry, since most people start fresh out of school and burn out of the industry in less than five years.

My manager got laid off as well, who was in his 60s, did excellent at his job, and had tons of amazing experience (I wish I worked on even just one of the cool games he was lead on), but it was definitely because he was one of the highest paid people there (if not the highest), not because of anything else.