Ball pythons reach sexual maturity between 18 months and 4 years of age. The recommended size for a male seems to be 800g. There are varying opinions on how much a female should weigh. I've heard 1500g recommended most, but it probably wouldn't be a bad idea to wait until your female reaches 2000g to be on the safe side. I am personally shooting for 2500g+ as I think the extra weight is worth it for larger clutches and/or hatchlings.