I’m not sure if it’s an established fact or just decent modern research but… they can’t die of old age. There are plenty of diseases and hazards which is a dice roll every day but no difference in those events for a 5 year old or 150 year old.

A quick google… discovermagazine.com/2002/jun/featturtle

“Blanding’s and perhaps also Midland Painted turtles don’t senesce— deteriorate physically— as they grow old. They simply don’t age. And Congdon says the females actually produce more eggs as they grow older: “They’re crankin’ compared to the young ones.” When they do die, the cause is often an attack— hit by a car or mauled by a raccoon— or one of a number of infectious diseases that kill these turtles at all ages in seemingly equal proportions. While certain ailments, such as cancer and heart disease, strike older humans more often than they do younger ones, Congdon’s animals don’t seem to become more vulnerable to disease as they grow older.”