A correspondent sends this citation from a physics textbook of 1937. Physics is basically a young man’s field. Even Einstein, with his flyawy gray mane, was just window dressing in his later years:

Bohr was twenty-eight years old when he published his first paper on the theory of the hydrogen spectrum. In fact, the quantum theory has been from the first to last a development by young men. Einstein, as already mentioned, wrote his initial paper on the corpuscular theory of light at the age of twenty-six. Heisenberg was twenty-four years old when he laid the foundation of the matrix mechanics. Dirac and Jordan wrote their first important papers at the ages of twenty-four and twenty-three, respectively. W. Pauli, Jr., was already a figure of importance in theoretical physics when at twenty-five he formulated the exclusion principle which bears his name. Uhlenbeck and Goudsmit were twenty-five and twenty-three years of age, respectively, when they invented the spinning electron. L. de Broglie published his first paper on the wave theory of the electron at thirty-one, while Schrödinger’s most important papers on wave mechanics were written at the relatively advanced age of thirty-nine. Of course the contributions of older men, especially Sommerfeld and Born, have been exceedingly valuable, but one cannot but be impressed with the importance to science of a system of education which enables young men to finish their preliminary training and start their career of productivity while the extraordinary mental energy of youth is still in full vigor.
The quote comes from footnote 3, on page 2 of The Fundamental Principles of Quantum Mechanics with Elementary Applications, by Edwin C. Kemble, First Edition, McGraw Hill: New York and London, 1937.

I wonder what today’s textbooks say. My correspondent points out that the fact of physics and math being a young man’s field argues against prolonged education. Also, he notes that the Fields Medal, often regarded as the highest prize in mathematics, must go to individuals 40 or less. And it has never gone to a woman. We’re back to young men.