The International Congress of Mathematicians (ICM), a quadrennial conference dating back to the 19th century, kicks off today in Philadelphia, PA, USA. The highlight of the opening ceremony is the announcement of a new cohort of Fields medalists. The award is often described as the Nobel Prize of mathematics, but Fields medalists are conspicuously younger than Nobel Laureates, who typically conduct their award-winning research in chemistry, economics, medicine, or physics in their mid-40s and receive the award decades later. Mathematicians are only eligible for the Fields Medal until the year they turn 40. Why is mathematics' highest honor reserved exclusively for the young?