By MIKE SCHNEIDER, Associated Press Sorry, boomers. Millennials and their younger siblings and children now make up a majority of the U.S. population. A new analysis by the Brookings Institution shows that 50.7% of U.S. residents were under age 40, as of July 2019. The Brookings' analysis of population estimates released this summer by the U.S. Census Bureau shows that the combined millennial, Generation