Source Pope Benedict XVI is almost 86 years old, had a stroke in 1991 that reportedly temporarily affected his vision. He fell in 1992 and 2009, and also had either arthritis or arthrosis, a similarly painful and debilitating joint condition. His doctor also advised him against taking any more transatlantic trips. Here's what came in his resignation letter: Dear Brothers, I have convoked you to this Consistory, not only for the three canonizations, but also…