In my area, 40+ developers basically fall into two groups:

- Burnt out developers who still like their job. These people often have a background in some STEM field, may hold a PhD etc. They can be difficult to work with due to the odd outburst, but their approach to problem solving is pretty constructive.

- Burnt out developers who hate their job. This is the most difficult group of people to work with I've encountered in my career. These people struggle on a daily basis and cannot be properly integrated into a team.

Now, if I became a recruiter, I would be aware that hiring 40+ developers can be a gamble. I know I will probably be one of those guys some day, and I don't see a non trivial approach to solving it. The software industry simply sucks.