Evidence on school-entry age impacts in lower-income countries is limited. We assess how school starting age affects human capital development in Lesotho, exploiting an enrollment age threshold. Children who start primary school at older ages overcome initial skill deficits as they progress. They are more likely to remain in school, spend less time on economic and household activities, and obtain substantially higher total years of schooling. In adulthood they are more likely to have professional occupations and less likely to be married or have children as teenagers, become HIV infected (men), and experience the death of a child (women). (JEL I12, I21, I25, I26, J13, J24, O15)