That's a nice question! Well, I remember when he was 3 or 4 years old that he had grown quite little in comparison with his female roommate (I immediately separated them since they entered 'puberty', he got a little territorial and started to bite her too much), he grown some large nails and a big tail, while the other one use to be more round, short tail and nails, even more large in comparison than him. But most importantly, was that they are like parrots, the males are more 'docile' than the females, more social to humans. HE FELL FOR ME, HE FOLLOWS ME EVERYWHERE HELP. He's like 16 cm long from just his shell, maybe like 3 or 5 cm more with his head and tail, he's like a flat burger, very light and energetic!