I start breeding them when they hit 1600g (I breed year round). I do think its more complicated than a certain age/weight. Even though they are definitely large enough at 1600g, this doesnt mean they will go though. I had one female bred for the first time when she was 7 and a spider ovulate 30 days before her second birthday. So far I havent had any complications as long as the females are over the 1600g, even when they are young.