A new study shows that Americans under the age of 40 now make up a majority of the U.S. population. The finding came from an examination of detailed age data released by the U.S. Census Bureau. The examination was carried out by the Brookings Institution, a Washington D.C. policy and research center. The Brookings study found that people under age 40 made up 50.7 percent of the U.S. population as of July 2019. The percentage represented 166 million people. Older age groups numbered 162 million people. Many of the older people are considered “baby boomers” - people born in the years following World War II. They have long been an important group in America because of their large numbers. Many of the people under age 40 are in a group known as “millennials.” Members of the millennial group were born between 1981 and 1996. People in another group, the so-called “Generation Z,” were born after 1996.