Jonathan's age is essentially everyone's best guess, based on the available evidence.
His veterinarian Joe Hollins - seen in this video doing his best to scrub the fidgety tortoise - told sainthelenaisland.info in 2015: "We have a record that he was landed in 1882 fully grown. We are told that fully grown is at least 50 years of age, and so this is how we extrapolate back to a hatching date of 1832, and forward to a current age of 183. Life expectancy is 150."
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The freshly cleaned up animal is a Seychelles giant tortoise. Now blind from cataracts and unable to smell anymore, he is hand-fed by Hollins, who said in December 2015 that the wise old animal was "alive and well."
Every day forward is gravy for the ancient animal, it seems.
"There is a chance that he'll either drop dead tomorrow or live until he's 250 and see us all off," said Hollins.