with my small experience :
i am pretty sure
THERE IS NO WAY A 1000 GRAMS FEMALE BREED !
Might be possible but I hope no one try it ! There is more chance of unsucess and of death than anything else.
If the female is too young or too small don't breed her. 1500g is the minimum but 1800-2000g is the best.
Not because they reach 1500g that they are ready to breed. Just like it's not because a male reach 600g that he will reproduce.
Male can breed younger (less than a year happens), but that's usually not the case, and if he can get tired quickly and get in problems.