Seems their findings are that, to grossly oversimplify, some people just have a higher chance of getting sick than others, and that remains consistent from yout

Seems their findings are that, to grossly oversimplify, some people just have a higher chance of getting sick than others, and that remains consistent from youth to old age. And given how many chances there are to get sick, making it through 'the filter' to get to 100 is only realistically going to happen to those who are both lucky and have that low base rate of disease going for them.