As a general rule, females should be 3 years old, weigh 300g and be 3 feet long.
Males can be smaller, but 3 years old is recommended as they're likely to be 100% fertile by then. Males will breed successfully earlier, but have lower fertility and so it's a bit of a toss-up as to whether they'll achieve anything.
I like the male to be about the same size as the female, in case things get rough.
I've fund that egg clutch sizes tend to be smaller when the female starts breeding and gradually get larger up to about the age of 7 or 8. I've had first clutches of 6, and the largest clutches can be 20-30.