Out of the tiny percent of people who live to as long as 100, not that many of them live too much longer.
While living to 90 is technically above average, in the 21st century, it isn't uncommon and super-rare, especially in comparison to people living to 100.
http://www.theguardian.com/news/datablog/2011/aug/04/live-to-100-likely
http://www.businessinsider.com/social-security-life-table-charts-2014-3
For example, there is a conspiracy theory that Hitler didn't die when and how most people thought he did, and that he hoaxed his death and lived on in hiding many years later. Regardless if that is true or not, we can be certain beyond a reasonable doubt he isn't still alive today, because there have only been very few cases of people living that long, that suggesting it is beyond absurd, based on our knowledge of human lifespan. I'm just using that as an example-I'm not trying to get into discussion on conspiracy theories in the science forum.
The mathematical probability of even centenarians living to that age is very low. The oldest recorded case is 122, and even that is super rare among centenarians. It's interesting to note that out of the people who reach that very old age of 100,only a very tiny percentage live to become supercentarians, and only a few of them live many more years. But do you think there is a "cap" on the human lifespan-like an age that not even the oldest ceneterians can pass, or an age that there is only a 1 in millions chance?
My theory, based on what I've read about centenarians, is that without future intervention of science (and even then there may be limits), there is a maximum human lifespan that nobody can cross, and the vast majority of the human population, within certain limits, will have a lifespan that is much shorter than it. At the same time, I do believe there is a minimum lifespan. It is almost unheard of, probably 1 in many millions, for people who are young to just die from natural causes.