Source: Wikimedia commons / Marg.

Last month, the U.S. Census Bureau released its study, The Centenarian Population: 2007 – 2011, part of its American Community Survey project. The report profiled various characteristics of the 55,000 persons who have made it to the 100-year mark – and, in some cases, surpassed it: The overwhelming majority, 81%, is female, and only about 15% had attained a bachelor's degree. Interestingly, the centenarians who still work reported pretty decent mean earnings, at $51,000, while the over 65 contingent reported annual mean earnings of only $37,000.

As baby boomers move into their 50s and 60s, the notion of living for a full century becomes more plausible. What can the oldest among us teach boomers about living long – and well?

I spent some time tooling around the Internet, reading studies about and interviews with American centenarians. What I found supports the notion that these persons have a few key personality traits in common. Here are the major tenets that these individuals seem to live by.

Don't worry, be happy
A sunny, positive outlook and a general sense of well-being seems to be the recipe for a long life, according to geriatric studies focusing on long lifespans. In a 2006 study of nearly 500 Ashkenazi Jews over the age of 95, researchers expected to find that the participants lived so long because they were "ornery", but instead found that they were optimistic and outgoing, and loved to laugh. Another study that year by the Georgia Centenarian Study found that the participants in the research had a personality mix that was low on the neurotic scale, while having high levels of competence and extraversion.

Centenarians corroborate these findings. A woman interviewed while skiing on her 100th birthday told ABC News last year that being positive helped her get through whatever life handed out, while the 100-year-old author of Up the Down Staircase noted a couple of years ago that she considered humor "a life force".

Stay busy, keep working
Amazingly, 2.9% of American centenarians are still working, and making pretty good wages, to boot. Though continuing on with paid work this long after the traditional age of retirement isn't for everyone, most 100-year olds advise others to stay busy at something that they enjoy.

Irving Kahn, one of the participants in the aforementioned longevity study on Ashkenazi Jews, still works each day at the brokerage firm he founded with his family in New York. In New Jersey, 100-year-old Agnes Zhelesnik continues to teach home economics full time, while Dr. Fred Goldman of Ohio still worked as a physician after turning 100 in 2011 – even making house calls.

Even if centenarians don't continue paid work, they advise others to do something interesting each day and to continue learning new things.

Other factors, such as genetics and lifestyle, also contribute to longevity, of course. But the overwhelming evidence that attitude can influence the length of one's lifespan is worth noting.

If you are worried about outliving your retirement funds, ponder this: while 17% of centenarians were considered to be below the poverty line, that percentage is only slightly above the 2012 national average of 15%. Considering the fact that life expectancy is only 78.7 years, most 100-year-olds were able to successfully cope with an extra 20 years or more of life without becoming destitute.

Did their positive outlook help them to plan their retirement more effectively? It certainly is something to think about, no matter what your current age might be.

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