I think there are definitely a few things which determine average life expectancy in terms of biology, and Neuronal Stem cells are only one part, at the DNA level you have telomeres which break down as we age (more so in men than women hence why women live longer), Telomeres protect DNA from alterations and from degradation and hence as we age and they degrade, we also begin to degrade and thus 'age'.

Nevertheless I just want to say that your article is brilliant, in terms of the impact on society I believe that (If you compare to the bacterium analogy) as the age of the population is extended we will need to reduce the number of births accordingly otherwise there will never be enough resources and we will all die out (Just like Bacteria do when their resource:population ratio is less than 1).