From the report:
The United States, the third most populous country globally, accounts for about 4.5% of the world’s population. The U.S. population—currently estimated at 308.7 million persons—has more than doubled since its 1950 level of 152.3 million. More than just being double in size, the population has become qualitatively different from what it was in 1950. As noted by the Population Reference Bureau, “The U.S. is getting bigger, older, and more diverse.” The objective of this report is to highlight some of the demographic changes that have already occurred since 1950 and to illustrate how these and future trends will reshape the nation in the decades to come (through 2050).
Aging & Longevity > Demographics
Congressional Research Service (CRS)