Is it true that you can age a tortoise by counting the rings on its shell, in a similar way to a tree trunk?

Unfortunately, this is not reliable method of aging these reptiles. Young tortoises for instance often have several rings evident on their shells by the time they are a year old, which would suggest they are actually older than is the case.

On the other hand, you frequently find that the shells of adult tortoises become smoother, with signs of these concentric rings disappearing in old age. This applies particularly in the case of those such as the American gopher tortoises (Gopherus species) (above) which burrow underground, as they rub their shell regularly on the sides of their tunnels, obliterating these patterns as they move in and out of their retreats.

But just as with a tree's growth rings, the shell of the tortoise does give some clues as to its past. When food has been plentiful, the tortoise grows rapidly, and as a result, the spacing between the concentric rings on the shell will then appear wider.