Turning 100 isn’t such a big deal anymore. That according to a recent Associated Press article. America’s population of centenarians 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. Experts attribute the rise in 100-year-olds to better medical care and the dramatic drop in childhood-mortality rates since the early 1900s. They also have good genes on their side and have made common-sense health decisions, such as not smoking and keeping their weight down. Get the lesson?