Did the federal ban on mandatory retirement policies negatively impact faculty diversity? In recent years, there have been substantial increases in the representation of women and Black and Latino graduate students, but this has not translated into proportionate changes in faculty composition. I examine a previously understudied change, the 1994 federal ban on mandatory retirement policies, to explain why faculty diversity remains so low. Prior to the ban, most professors were required to retire by age 70. While this policy change was an important step towards reducing age discrimination, it occurred during a time when the majority of professors were white men. A recent study of law schools showed that lifting mandatory retirement resulted in an increase in the average age of professors. I hypothesize that if the average retirement age of professors had not increased, that racial/ethnic and gender diversity among faculty would have increased significantly. Using restricted access panel data from the National Center of Education Statistics’ National Study of Postsecondary Faculty as well as data from the National Science Foundation’s Survey of Earned Doctorates, this paper provides causal explanations for long-standing inequalities in the academy.