Age and size of the female is the big factor in breeding. There colors will change once they mature and the female should be 12 months old plus before breeding to ensure she is fully developed and large enough.
Like Nick said, you should wait until the female is at least 1 year old before breeding her. When the female is receptive she will have turquoise dots. When you see this, the female is ready to mate and you can introduce her to the male then.