Interesting point about the German. Do we know for sure that it wasn't actually the original? Since he is, after all, a German speaker.
Whether it's only one kind of strength or both, it's hardly surprising -- very few people would even try to do such a demanding job at his age. I think that's another problem with those anachronistic models that assume life tenure, like, indeed, the monarchy. Certainly a few people can still do some of the work in their 80s, but unless they're extremely physically active, most have to admit they work and think at a slower pace, and need more rest and more assistance from colleagues. That model surely works better in more cooperative, consensus-based contexts than in ones that grant one person sole and absolute authority -- but unfortunately, it's that imperial, authoritarian model where such absolute power persists in conjunction with unlimited tenure. Fortunately most of the other monarchies in the world are more ceremonial than decision-making.
I was impressed when the Dutch (IIRC) queen recently abdicated at a normal retirement age in favor of the next generation -- indeed, 'retired' would be a much more user-friendly word for it -- and I appreciate the pope's having finally taken this step, even if it might have been better to do it still earlier. I hope he can still read and play the piano and so on in his retirement, and I hope future popes will follow his example and retire earlier.
Even Castro, actually, stepped aside, and good for him. Now all we need is someone to admit the truth with regard to Chávez. The sad thing is that the authoritarian system itself evidently provides great motivation for the people at secondary levels to cling to power vicariously, because their own power is so tied to an individual.