Not sure I understand the paper (not my field); are they saying that extrapolating from a mortality measure predicts that mortality is inevitable? If so... isn't that just a way of confirming the obvious, viz. that higher quantiles of a logistic distribution are closer to 1? Finding a cutoff age at a - quite large, it seems - number of 120-150 years is cool and all, but I don't see how this informs us about anything other than mortality measures predicting eventual mortality?