On a male if the claspers are rolled he is good to go!! I am finding in my collection that for the females it is age that is determining sexual maturity. The average for my lot is about 18 months old the females can become gravid.
That sounds about right. Size really does not matter. Probably between 12 to 18 months before he is fully rolled. You will definitely know when it is time. His demeanor will change around the female "if things work out" I put that in parenthesis because not every male and female will pair off. That is one reason I keep 2 females to one male. The other reason is it helps to keep the male aggression down. Anyway now that I lost track lol the male will definitely start chasing the female around, and you will notice his interest in her become much more prevalent.
My male just turned 2 in August and is 12 inch. His claspers got huge and rolled maybe 3 months ago. I could barely see his claspers till he was about 1.5 years old.
That being said he is chasing and biting the female just recently with in the last month or so. He is a black.