Females are ready to start pairing at 1200grams. If they go they will eat like a horse and gain weight like no other.

My 09 females are 1400grams now since pairing and gaining weight like mad. Its your snake you know when shes ready to breed. 1500gram rule most follow is not a "they mature here" or 3rd winter stuff. They will mature when they are ready and will not hurt to try when 1200+. They continue to gain weight throughout breeding so starting off lighter weight, will not harm them as they will gain through the many months of breeding.