I'm close with someone who was offered a position at a nuclear startup NuScale, that aims to manufacture cookie-cutter, modular nuclear reactors, where you scale the power plant by adding more reactors over time as your needs change, and ship the old spent ones off.

As I understand it, part of the problem in hiring is that for a nuclear startup you really need experienced engineers as you go into producing working prototypes. Depending on the position, they don't necessarily need explicit nuclear experience - my relative didn't have it - but they do need a proven track record of not majorly screwing up ever, and that requires experience you can usually only get working for years in real engineering environments. There can be no 'oops, we messed up the privacy requirements' apology or people die, meltdowns happen, and the company gets the biggest of red flags.

That's not to say you need to be old to start a nuclear company, but that you will probably need to work with older engineers, who are harder to hire, settled in their jobs, and scattered across the US, with mortgages, families, and the like.