[kobeya]

First, I don't think you are adequately compensating for the availability of new technologies, such as medical molecular nanotechnology, which we will certainly have by 2065. The entire approach to medicine that we use now is likely to be obsoleted in that time frame, leading to the eradication of most terminal diseases.

Second, one doesn't have to eliminate biological death entirely to muck up those forecasts. We know from super-centenarians that those who are lucky enough to not suffer any life threatening conditions nevertheless kick the bucket around age 120. Even if that's not fixed by 2065, it's almost double the average life expectancy and that is not factored at all into the OP's calculations.

Third, birthrates are currently constrained by menopause in women. Most women don't have more than a few children in the developed world because they are biologically incapable of having more. And although men have the capability to have "2nd families" (with another woman later in life after their previous children are grown), women do not. Defeating/controlling menopause is therefore more likely to result in either larger families, women choosing to have a second family at a later stage in life, or women who would have otherwise missed their chance having a family at all. Again, fertility advances are not factored into the OP's calculations.

Thus although I could argue that biological immortality is not "unfeasible", I don't need to. The OP has failed to factor in reasons why the death rate will go down and the birth rate will go up, making his charts too conservative.