It's not ageism, it's amount of experience. Age simply provides a cap on how much experience you could possibly have. Or do you believe that managers and leaders gain nothing from practicing their craft longer and in a wider variety of situations?
> Age simply provides a cap on how much experience you could possibly have.
Not really. It depends on the opportunities and luck to meet the right people at the right time. Plus, people internalize experiences with different speeds. So, while in general you're right, you need to account for outliers that lived a particularly lucky life.
Though to be fair, people who got mountains of experience that way despite being young do not, in general, see themselves as next Jobs.