What is the maximum age someone can be when winning the 'Fields Medal' in Mathematics?

But why that age? You didn't explain that at all. On the face of it, it appears arbitrary and openly discriminatory. Why forty? Why not fifty? Or seventy? I could understand twenty, as in a youth award, but if it's so prestigious, what happens when you give the award to a thirty-nine-yaer-old mathematician for a rather mundane (yet excellent) observation, but a forty-one-year-old comes out with today's Theory of Relativity? The award is a joke! There is no prestige in excluding any class from a "most prestigious" award. Just change the excluded group with another class of oppressed people, and the ugliness becomes apparent. Example: "The Fields Award is the most prestigious award in mathematics. It is offered to each year's most accomplished mathemetician who isn't Jewish." I rest my case.

I don’t get the age limit.