Would it be possible to triple the life expectancy, as it happened in the last 3 centuries? Well, as I pointed out the "average" life span was tripled but there were people 2000 years ago who reached the age of 80 and even 90... but they were just very very few. The average has tripled but no one today is living to be 240 years old.
There seems to be a cut off age beyond which we cannot go. And, statistically, this seems to be around 114-115 years old, even though the present certified record is 122 (see photo).
One would think that we are "programmed" to have a certain life span and we cannot exceed that. And, to a certain extent scientists have found out it is, indeed, the case, and not just for our species but for the many species that have been studied.
It is not just the second law of thermodynamics at work, the increase of entropy that over time disrupt the order of living beings. If that was the case one could assume that all living beings would have a similar life span, and this is not the case. Mayflies live just one day, some species just a few hours, the time it takes to mate and lay eggs (not counting the time they spend as nymphs); at the other end of the spectrum plants can live several millennia, yeast for several million years (most of the time spent in "suspended" state).
It seems that each species has a sort of internal clock that dictates its life span. Interestingly, scientists have proved that it is possible to stop the clock and more recently they have shown the capability of rewinding the clock, that is of rejuvenating a living being.
Several scientists are convinced that in principle there is nothing that would preclude rejuvenation in our species as well, we are no different from other multicellular species, like mice, where experiments have shown that by lengthening the telomeres and using "updated" stem cells you can increase their life span by 30% and actually cause a rejuvenation of their cells.
A 30% life increase would mean to push the average life span from 80-85 to over 100.
Some, like Kurzweil, are advocating a future where death will no longer be a given. And for them this future is not that far away. Actually, Kurzweil believes that in 2050 we will be, technologically speaking, capable of extending life beyond any boundary.
One of the reason is the progress being made in the creation of organs. Today it is commonplace to create skin and some bones in the lab and then implant it to a patient needing it. More complex organs like a trachea or a bladder are being experimented (artificial trachea transplant have been performed starting in 2011 but there are some questioning the protocol used) and even more complex ones are being actively researched.
Lung, heart, gut are within the scientific possibility although it will take few more decades. By 2050 it may be reasonable to predict that it will become feasible to produce and transplant these organs. Brain transplant, on the other hand is pure science fiction and it is not on any scientific roadmap. There are, however, promising studies to fix brain pathologies, including Alzheimer.
It is really difficult to predict a significant increase in human life expectancy, in the order of 30% or more, by 2050, however we are now learning more and more about the mechanisms that regulate the life span of several species and this understanding opens the door to "a cure" for what has always been considered the "incurable disease" per excellence: ageing.