We shed new light on the linkages between age diversity and technological innovation, and explore the moderating effect of human resource practices on such relationships. Based on a linked dataset that contains cross-sectional survey data and longitudinal employer–employee data from Luxembourg, we show that the effect of age diversity on innovation depends on the age distribution pattern of employees: positive for firms characterized by heterogeneous age groups (variety), negative for those dominated by polarized age groups (polarization). HR practices such as information sharing mitigate the adverse effects of age polarization on innovation. Practices enhancing development such as training are found to play a significant and negative role in moderating the relationship between age diversity and innovation. We illustrate how academics and practitioners may use HR practices within the context of a heterogeneous aging workforce and the age-related differences in values and abilities between generations.