There is no scientific basis on which to estimate a fixed upper limit. Whether 115 or 120 years, it is a legend created by scientists who are quoting each other. It is not a biological constant. Whether or not this can go on indefinitely is difficult to say. There is no hint yet that the upward trend is slowing down.
Human progress is real, somehow.
We are changing the limits of human life span over time. A spokeswoman for Age Concern said attitudes and government policy would have to change to cater for a population that was living longer. We are already having to change our ideas about retirement as people are living longer. The study is published in Science journal.