Number of 100-year-olds is booming in US

But turning 100 isn't such a big deal anymore.

America's population of centenarians - already the largest in the world - has roughly doubled in the past 20 years to around 72,000 and is projected to at least double again by 2020, perhaps even increase seven-fold, according to the Census Bureau.

The Census Bureau estimates there were 71,991 centenarians as of Dec. 1, up from 37,306 two decades earlier. While predicting longevity and population growth is difficult, the census' low-end estimate for 2050 is 265,000 centenarians; its highest projection puts the number at 4.2 million.