The claim’s implied causal chain is: the stress/tempo of market-making makes older traders unable to keep doing the job, so it is mainly a “young man’s job.” The evidence does not establish that. OSHA notes that workplace stress can hurt job performance and physical functioning in general, so the pressure mechanism is plausible. But a study of London high-frequency traders found that age was not a significant predictor of trading performance once experience was included; experience mattered more. And the closest BLS occupation data I found, for securities, commodities, and financial services sales agents, shows a median age of 41.7 in 2012, which does not look like a uniquely young occupation. Overall, the available evidence is too thin and mixed to support the broad age-based claim. Sources: OSHA Workplace Stress (https://www.osha.gov/workplace-stress); U.S. Bureau of Labor Statistics, “Employed persons by detailed occupation and age, 2012 annual averages” (https://www.bls.gov/cps/aa2012/cpsaat11b.pdf); Coates et al., “Second-to-fourth digit ratio predicts success among high-frequency financial traders” (https://users.econ.umn.edu/~rusti001/Research/Neuroeconomics/2D4D.pdf).