Centenarians are different from the rest of us, and it's not just that they are a lot older. They are a select group, having persisted through wars, diseases, disasters and accidents that kill tens of millions of ordinary mortals every year. 

In looking at what makes a 100-year-old so special - fewer than 2 in every 10,000 Americans live to that age or older - those who study aging cite factors like genetics (particularly having two X chromosomes, as 85 per cent of centenarians are women) and environmental influences like good nutrition and health habits. 

But a statistical study of centenarians by researchers at the University of Chicago has found some other potential predictors of extreme longevity. Women and men who were the first born in large families, the study found, were two to three times more likely to make it to 100 than later-born children. 

Those raised in the rural West had a better chance of reaching that age. And people of advanced age who were born in October and November had longer life expectancy than those born in April through June. 

So if you are a fall baby, the first child of a farming couple from Boise, are you a safe bet to make it to 100? Hardly, experts say. Factors like birth order and birth month play a small role, at best, in the likelihood of reaching advanced age, and are overwhelmed by others.