I am not great at guessing the age so much. Pics can sometimes be deceiving and every chameleon is not always the same size at a given age. That being said, I am guessing maybe 8-10 mos or so. As far as the cage, it is ok to put a female in a male size cage. Nothing wrong with giving them as much room as possible. Also, you are going to have to put a laying bin in the cage so you will need something with some room to do so. I am guessing you are aware about the females laying infertile eggs?