Running around analyzing the genetics of supercentenarians isn't really all that useful from the point of view of making people live longer. Doubling a tiny chance is still a tiny chance, and their longevity has a lot more to do with randomness than with anything else.
Perhaps more interesting is asking why these people die, what are the causes. Different ages are characterized by a different prevalence of disease; cancer hits a maximum mortality rate and then fades as a major cause in the oldest old, for example. From the few autopsies performed, supercentenarians appear to predominantly die of senile systemic amyloidosis, a clogging of the cardiovascular system with misfolded transthyretin that appears to play a lesser role in heart failure in younger old age.
If we want to ask why human life span seems to have a rough upper limit (though 50%+ yearly mortality for any combination of causes is going to look a lot like a hard limit when stretched over 20 years), then this form of amyloidosis seems to be one of the places to look.
Interestingly, this form of amyloidosis has an inherited version that shows up in young people, so despite the institutional reluctance to work on medicine to treat the causes of aging, there are actually a number of therapies in development and trials, some of which can selectively remove this form of amyloid. At some point the research community will wake up to this form of amyloid being a contributing cause of heart failure (a process underway judging by recent papers on the topic), at which point we might well see a leap in the observed upper limit to human life in the decades following more widespread use.