Want your kids to celebrate their 100th birthday or beyond? Then you may want to have them before you hit 25.

Researchers from the University of Chicago's Center of Aging have found that a child's chances of becoming a centenarian double if the mother was younger than 25 when she gave birth.

The father's age was deemed less important, said Leonid A. Gavrilov, who co-authored the study with his wife, Natalia Gavrilova. (They are both research associates at the center.)

Other factors they said may help a child reach 100: growing up in the West, spending part of one's childhood on a farm and being firstborn.

Their study, supported by the National Institute on Aging and presented last month to the Population Association of America, drew on data from about 198 centenarians born between 1890 and 1893.

Among theories Gavrilov offered to explain the findings: a woman's best eggs are fertilized first; younger mothers are likely to be healthier and less subject to career demands; the care from a younger mother may be better or longer-lasting.

But Gavrilov said that all theories were speculative and needed further study.

The research, he added, was not meant to suggest that young women rush out and have kids.

However, Thomas Perls, director of the New England Centenarian Study, an ongoing study of more than 1,000 people, isn't buying the Gavrilov/Gavrilova report.

Perls, an associate professor of medicine at the Boston University School of Medicine, questioned the validity of the data used, noting that the findings have not been published or subjected to peer review.

He also criticized the study for failing to consider such factors as the mother's marital or financial stability or access to healthcare.

The key to improving the odds of longevity, Perls said, lies in a combination of environmental and genetic factors. These generally include not smoking, weight control and access to better healthcare.