How do you know the age of a turtle?

Turtles are considered one of the longest-lived animals, and the age that a turtle can reach depends on its species, for example, the giant Galapagos Islands tortoise can live for more than 100 years.[1] The average lifespan of sea turtles is between 80-100 years, and needs between 20-40 A year to reach sexual maturity, box turtles, and land turtles can live for 50-100 years, and scientists assume that some colored turtles may be able to live for 300 years, although it is difficult to verify the validity of this hypothesis.[1] It is worth noting that there is no definitive way to determine the exact age of a turtle, but there is more than one way to estimate the approximate age of a turtle, including:
1__the size
2__sexual maturity
3__The number of rings in the tortoiseshell
4__The number of tortoiseshell scratches