Abstract: Using a comprehensive euro area regional dataset and exploiting exogenous variation in government spending, this paper shows that population aging significantly amplifies fiscal policy effectiveness. On average, a ten-year increase in median age raises the regional fiscal multiplier by about 38 percent. This effect is heterogeneous and shaped by institutional features, in particular the generosity of countercyclical transfers and the degree of age-based labor market segmentation. In regions with less generous benefits or weaker age segmentation in employment, aging has a muted—or even negative—effect on the fiscal multiplier.