How long will he be King? (Any guesses?)

Assuming he doesn't abdicate and the monarchy remains, how long will he be on the throne? If we tally up the life span of his mother and father, and his grandfather and grandmother (on both sides), we get an average life span of 83 years. His grandfather King George VI died fairly young (56), as did his paternal grandfather Prince Andrew of Greece and Denmark (62). The Queen Mother died at 101, Prince Philip at 99, and Queen Elizabeth at 96, while his maternal grandmother Princess Alice of Battenberg lived until 84. So, it's somewhat of a mixed bag, but the trend does seem to be towards longevity. So, it is more likely than not that Charles will live at least another ten years, perhaps considerably longer. This also means any heir could also be fairly old by the time they get the throne