In this paper we investigate the changing demography of neighborhoods. We focus upon the dynamics of the age structure of neighborhoods, paying particular attention to the roles of (a) the magnitude of mobility and (b) the age composition of in-migrants and out-migrants. A model for studying the changing age composition of neighborhoods is developed, and alternative scenarios characterized by the nature of in-movement and out-movement are examined to make statements about the age of householders in neighborhoods. We find that high rates of mobility may serve to bring about a relatively youthful equilibrium age structure quite rapidly, whereas low rates lead to a higher mean age and to damped harmonic fluctuations both in the mean age of householders and in the magnitude of the age heterogeneity of the neighborhood. In addition, we compare the evolutions of age structure in neighborhoods with age patterns of in-movement and out-movement that could typify areas of renters and areas of homeowners.