Many Indigenous Nations speak of turtles living to 1000 years. Indeed there are a few verified stories of turtles kept as pets of generations of Emperors that indicated turtles live well over 100 years; and even a verified story of a snapping turtle that was brought in to a veterinary clinic for treatment where a musket ball from the war of 1812 was discovered within it's body, indicating the turtle was over 200 years! However, only one aging study of sufficient size and duration has been conducted; and that study has been conducted in Ontario, Canada.
Turtles grow at different rates according to the climate that they are in, which is related to the level of nutrients found and the growing degree days available. Growth rates and aging is measured by carapace length (the length of the top shell from along the turtle's spine). Generally, turtles grow quickly when young and exponentially slower as they age. It is far easier to measure growth in larger turtles, such as common snapping turtles than in smaller turtles such as painted turtles.
In Algonquin Park, Ontario, Canada, the largest and longest (if not only) turtle-aging study was conducted by Dr. Ron Brooks and Dr. Douglas Armstrong over a period of 40 years and which as continued for more than 70 years. The study shows that turtles likely live well beyond 200 years old; with smaller turtles living beyond 400 years. Within the study growth charts are provided to indicate general trends in carapace size to age of turtle. Check out their incredible research here:
Armstrong Brooks - age estimation