Not in my experience. There's plenty of people under 40 in the defense industry. Every big defense contractor has internship programs to feed people in fresh out of university. And once you're in, it can be difficult to get out, since the pay is above average for the regions (and the benefits are glorious), but the workload is so light. It's not unusual to be on a project that's going nowhere for four months, so you get to come in and do busy work.

Hiring is tough right now, but it's tough for everyone. But that has lead to a huge increase in wages. Every one of my friends in the industry has seen promotions and 40% pay raises.

Not just guns but spy satellites. You can spend your whole career in defense and be directly responsible for exactly 0 weapons, just helping to find things in satellite images or make sense of signal data or help naval vessels communicate better

For older workers it can actually be easier because people move a lot in their 20s. A worker in their 40s might only have to list 3 addresses where a kid 2 years out of college might have to list like 5--one for every dorm and their parents and their first apartment