While the scute rings can help in estimating age, it is not "turtlely" accurate. The rings are more related to growth than to years, and for many turtles, the top layers of the scute wear away or are shed. Experts use a combination of knowledge of each species, scute rings, shell wear, general size and health, all combined to make a good guess about age, but it often winds up being fairly general, such as "mature", "old", or "very old." Some turtles can live to be well over 100 years old, which can make it very difficult to get an accurate age.