When most people think about living long, living to the age of 100 or more is not usually what they have in mind. And believe it or not, nor was it likely expected of most centenarians either.

But when you are among the longest-lived people on the planet, you are routinely asked how it happened. Most of them are as surprised as anyone that they’ve lived as long as they have, and rarely do they have any idea how they did it.

It’s certainly an intriguing topic, with both a fast growing group of people to study and experts ready to report the findings. It’s estimated 85K centenarians populate the United States today, and it’s expected that number will explode to over 150K within the next ten years and well into the millions as the baby boomers get on deck. The Center for Disease Control and Prevention recently reported that the number of centenarians has doubled in the last 20 years and the chance of living to 100 has increased 43% in the last 10 years. And it’s projected that one in three girls born today will see their 100th birthday!

Aging experts have also identified a new group of longevity-ites: Super Centenarians, those over the age of 110.  It’s estimated there are just under 100 in the U.S. and about 300 worldwide.  Obviously a considerably smaller group, our chances of being part of this special birthday club is about one in six million for us mere mortals and about one in 1,000 centenarians will hit this magic mark.

While there is growing interest in all aspects of living long, researchers specializing in centenarians believe genes likely play a more dominant role than lifestyle. The hypothesis is that a set of genes protects centenarians by delaying aging and preventing age-related diseases. Additionally, it appears to be a family affair as super-centenarians generally come from families whose members are also long-lived, so it’s likely in their DNA. In fact, men with a centenarian sibling were 17 times as likely to be centenarians, and women were 8 times as likely.

While it’s intriguing to discover the role family DNA may play in our chances of living to 100 or more, we have to get to 100 first, and for that we know our lifestyle indeed plays an important part. Regardless of how long we live, it’s how we live long and our quality of life that really matters most. So it’s not how old you are, but rather, how are you old that can truly make the difference between living and existing.