Otherwise it would be old people game.
Yet, is it perhaps possible that this position may signify a person possessed of a wonderful opportunity to become more educated? The Fields Medal is not intended to be the capstone recognition of a mathematcian's career any more than the Clark Medal is in economics. It's intended to award outstanding achievement for a younger contributor in a field that infamously tends to worship the more senior. The IMU awards other medals as well, including one for lifetime achievement.
In short, you're completely right to be bummed out! But perhaps you could take this glorious opportunity to learn more.
You didn't mention one, beyond saying that it exists or that it's given in special circumstances... Which is the challenge re:Fields being the most prestigious.
https://en.wikipedia.org/wiki/Albert_Einstein
https://en.wikipedia.org/wiki/René_Descartes
https://en.wikipedia.org/wiki/John_Forbes_Nash_Jr.
https://en.wikipedia.org/wiki/Alan_Turing
https://en.wikipedia.org/wiki/David_Hilbert
I think this rule is just wrong. Some mathematicians come from privilege, some do not. Even for the ones who do, it's rare that they come from _great_ privilege for the time. They are the children of mayors, not kings -- professors and engineers, not the financial aristocracy.We tend to celebrate achievement, not talent.
This may correlate well with elites since they have more opportunities.
I think the downvotes come from your sentence about significant developments going under reported. I don’t think this happens at all. If someone discovers something great or profound in math no one cares about the age of the discoverer. Wiles was given a special prize because he was past the age of 40 when he proved Fermat's Last Theorem.
When the mathematical knowledge increases, does the general character of the mathematical problems stay the same in the terms of required work and time? It's possible the problem set that young people can solve before they turn 40 will decrease after some time.
Edit: Let me address the down votes / polarization on this comment: Ageism in the most esteemed prize of a particular field seems obviously wrong to me. Is there a better alternative available? (That said: kudos to the winners! Truly great achievements all around.)