I've had 1200 g females lay eggs just fine. It's really up to you, but most folks say 1500 grams minimum. I think it has more to do with size than age. If the female is not mature, she wouldn't ovulate, but size is another matter. Maybe give her a bit more time, til she gets up to 1500grams.
I recieved some ball python females that had just laid, and they were under 1000 grams each. That's SMALL!!!!