The purpose of the study is to test the efficacy of alternative measures of "age of settlement" in explaining the structure of urban and metropolitan areas and the socio-economic characteristics of their populations. That age of settlement is related to other urban variables is well established in the literature. Although the conventional measure of age, the number of decades since a city attained 50,000 population, has been widely criticised as too crude and unnecessarily dependent upon size, no systematic comparison with alternatives has been undertaken. This study proposes several alternatives, including a novel weighted average of the time periods during which population growth accrued. Age values and ranks by age will be calculated, using alternative measures, for nearly 400 U.S. cities. The power of the alternative measures to explain dependent structural and socio-economic variables will then be tested and compared by estimating alternative multiple regression equations, using each age measure together with other independent variables. The use of refined measures of age is expected to clarify the independent influence of the age factor. City age is known to be an important determinant of the socioeconomic differences between central cities and their suburbs that currently create many problems of social policy. A clarification of the influence of age as compared with region, size and other variables will therefore be helpful in the formulation of social policy, especially in the areas of poverty, employment, housing and health.