If that confuses the less mathematically minded among us, here is a chart.

It's struck me as rather sweet that our cats, on reaching the age of twenty-one, would qualify for a telegram from the Queen (if there still were such things). And, for all those people who think I have been hugely optimistic in providing a chart that goes up to the age of twenty-four, I should say that I remember with some affection Stevie, the oldest participant in my Elderly Cat Survey, at the grand age of 26! It all goes to show what a huge impact diet, veterinary care and housing have on longevity in the pampered domestic pet when you consider that the feral tomcat has an average life-span of five years.