This paper studies how demographics affect aggregate labor market power, the urban wage premium and the spatial concentration of population. I develop a quantitative spatial model in which labor market competitiveness depends on the demographic composition of the local workforce. Using highly disaggregated administrative data from Germany, I find that firms have more labor market power over older workers: The labor supply elasticity decreases from more than 2 to 1 from age 20 to 64. Calibrating the model with the reduced-form elasticity estimates, I find that differences in labor supply elasticities across age groups can explain 4% of the urban wage premium and 2% of the spatial concentration of population. Demographics and skill together account for 10% of the urban wage premium and 2% of agglomeration.