Final answer:
The statement is true. The U.S. population has been aging significantly over the past century, with the proportion of seniors (over 65 years of age) tripling and the proportion of young people dropping by over one-third.
Step-by-step explanation:
The statement is true. The U.S. population has been aging significantly over the past century, with the proportion of seniors (over 65 years of age) tripling and the proportion of young people dropping by over one-third. This trend is supported by data from various sources, including the U.S. Census Bureau, which shows the increasing size of the age group representing ages 65-84.