You can not always go by the weight. I have 3 or so females that are 3-7 years of age and 2500 grams plus that will not be breeding this season. They are to small. Then I have a 6 years + female that is approx 1368 grams and she will be breeding this season.If you get the females and raised them from babies they should be ready to breed by there 3rd winter. Some do it sooner. I have results will vary. Some females are just bigger than others and will go sooner than the rest. Some are small like the 1368 gram female she will go but she also has small eggs and the babies hatch out small.
Nothing beats hands on experience or trial and error. Make sure the female looks thick and full bodied. If they look the least bit skinny do not breed them.
Good luck this season.