Economists have identified a substantial adult wage premium attached to high school leadership activity. Unresolved is the extent to which it constitutes human capital acquisition or proxies for an "innate" unobserved skill. We document a determinant of high school leadership activity that is associated purely with school structure, rather than genetics or family background--a student's relative age. State-specific school entry cut-offs induce systematic within grade variation in student maturity, which in turn generates differences in leadership activity. We find that the relatively oldest students are 4-11 percent more likely to be high school leaders.