Final answer:
The fastest-growing population segments in the United States are the elderly, specifically those aged 65 and over, as well as the Hispanic community, driven by longer life expectancies and immigration.
Step-by-step explanation:
The fastest-growing segment of the population in the United States today encompasses the aging population and the Hispanic community. The population aged 65 and older has seen significant growth, doubling over the last 50 years, and this is attributed to an increase in life expectancy and the aging of the baby boomer generation. Furthermore, within this elderly segment, the fastest growth has been observed in people aged 85 and older. Another noteworthy expansion is within the Hispanic population, which doubled from the 1990 to 2000 censuses and continued to grow significantly due to both immigration from Latin America and higher fertility rates compared to non-Hispanic groups.