So you're taking information from a source purely pertaining to the British Isles, and applying it to all of Medieval Europe?
I'm pretty sure that during this time period Continental Europe had much more contact and trade with the east, and thus were much more likely to have longer lifespans than those living in the British Isles.
Furthermore, your 'source' is a blog by a historical fiction and fantasy writer, not a true historian. Shall I continue?