Hi,

in adults you see much more pronounced femoral pores in males. Also females are of a darker colour-but that is obvious only, if your animals are from the very same area.
To my opinion, 40 g is way too small. These lizards need space to move. Otherwise this species tends to become extremely immobile and obese. To my opinion a ground space of 4 x 3 ft is about the very least for a pair of G. major.

Ci@o

Ingo