I would think they are more willing to spend time on something hard (and that they don’t know is impossible, see the book Uncle Petros and Goldbach's Conjecture

I would think they are more willing to spend time on something hard (and that they don’t know is impossible, see the book Uncle Petros and Goldbach's Conjecture). Older people have to actually make progress in their careers and make money so they are much more hesitant to “waste” time on a major open problem.