According to the MayoClinic, irritability can be a sign of diabetes. According to the American Health Assistance Foundation, irritability in seniors can be a symptom of Alzheimer's disease. Or, as you so eloquently put it, it can be completely non-medical:

"We no longer luxuriate in expectation of untold sunrises; we can count them. This nearness to the end does not allow for much 'beating around the bush' and perhaps our resentment of this fact betrays itself in crankiness."

Of all the possible reasons, I plan on telling people that the reason for my crankiness is the one listed in the original article--the one that all of these comments are attached.

Wesley Hein
Wesley [at] lifetwo [dot] com