The U.S. Constitution mandates that a census be taken in the United State every 10 years. This is required in order to determine the number of seats each state is to receive in the U.S. House of Representatives. The Census Bureau collects data on age and sex to support a variety of legislative and program requirements. These data are also used to aid in allocating funds from federal programs and, in particular, from programs targeting specific age groups.”
Census 2000 Data