The share of the U.S. population over 45 grew by about 10% over the past 20 years.
"Due to baby boomers "aging in place," the population age 45 and over grew 18 times as fast as the population under age 45 between 2000 and 2010. All states and metropolitan areas are showing noticeable growth in their older and "advanced middle age" populations which, for the first time, comprise a majority of the nation's voting-age population.
Although all parts of the nation are aging, there is a growing divide between areas that are experiencing gains or losses in their younger populations. In 28 of the 50 states, and 36 of the 100 largest metro areas, the population below age 45 declined from 2000 to 2010. Yet in 29 metro areas, including Las Vegas, Orlando, Houston, and Atlanta, the under-45 population grew by at least 10 percent over the decade. "