Iv asked the same question before. From what i was told, theres no definate way to tell. With a Juvi, its usually by size and weight, that can give you a good estimate. Adults i think is impossible unless you get WC in which case you can bet they are no older than 2-3 years old (that seems to be the average age before dying in Madagascar) How can the pet shop not know the age of their stock? If i bought them from a supplier i would want to know the age before selling them in the shop. Its basics!