Longer life with younger mothers

This NIH study reported by E. J. Mundell is curious:

Society's oldest members are most likely to be born to its youngest mothers, new research suggests.
The odds of living to 100 and beyond double when a person is born to a woman under 25 years of age, compared to those people born to older mothers, according to one of the most rigorous studies on the subject yet conducted.

The study considered some other factors besides maternal age also:

But what other factors encourage "extreme" old age? Previous research by Gavrilov and his wife/co-researcher, Natalia Gavrilova, has uncovered some clues. For example, in research published over the past few years, they found that U.S. centenarians were more likely to come from farming families in the Midwest than from any other demographic.
They also discovered that being the first-born in a family meant a lot, boosting the odds of making it to 100 by nearly 80 percent.
"But nobody knew why that was -- sometimes in research you get answers, but you also get new questions," Gavrilov said.
So, he and his wife set out to solve that puzzle. They selected 198 centenarians from across the United States, checking and double-checking their ages using every form of documentation available. Comparing the centenarians' histories to those of their siblings, the researchers then analyzed the data to help explain the "first-born effect."
One theory -- that first-born children might have been relatively protected from pediatric illness because they weren't surrounded by disease-bearing siblings in infancy -- didn't pan out. "We found that even at age 75 it still matters that one is first-born," Gavrilov said. "It's a late-life phenomenon."
A second theory -- that first-born kids reaped the benefit of a relatively young, strong and productive father -- also fell flat. "We got the very clear result that the father's age wasn't important," the Chicago researcher said.
That wasn't the case for mothers. In fact, statistical analysis revealed that young maternal age at birth completely accounted for the first-born effect.

This is good reporting to keep these different hypotheses straight and explain why the data supported one instead of others.

Although the new research shows no effect for paternal age on survivorship in these offspring, an earlier study by the same authors found that paternal age made a lot of difference, at least considering the longevity of their daughters. Here is part of the abstract of Gavrilov et al. (1997):

The daughters born to old fathers 50 - 59 years lose about 4.4 years of their life compared to daughters of young fathers 20 - 29 years and these losses are highly statistically significant, while sons are not significantly affected. Since only daughters inherit the paternal X chromosome, this sex-specific decrease in daughters' longevity might indicate that human longevity genes (crucial, house-keeping genes)sensitive to mutational load might be located in this chromosome.

But this study was of historical families of aristocrats, so maybe they were missing some effects that are being caught in the study of centenarians. Or maybe paternal age used to make a difference and doesn't anymore? In any event, it's curious. If this were "mutation load" or other genetic effects, I would expect the age of both parents to make more of a difference. And the combination of older fathers and older mothers may have changed over the years, which adds another complication with respect to mutational effects. This may be a tough one to work out.

References:

Gavilov LA and 8 others. 1997. Mutation load and human longevity. Mut Res 377:61-62.