The United States is in the midst of a demographic transition toward a population age structure with a higher fraction of elderly individuals. The associated growth of transfer programs for which the elderly represent most of the beneficiaries, such as Social Security and Medicare, will place upward pressure on the size of the public sector. The rising number of individuals who are beyond the traditional age of retirement, relative to the number of individuals of traditional working age, will create incentives for longer working lives and for greater investments in human capital by younger workers. Changing age structure may also affect rates of return available to savers, although these effects are likely to be modest.