I wait until they are at least 2 years old and 1500g. For example. I have an 07 female that is around 950g. I hope to breed her this year if she gets to 1500g. I have another 07 that is a later 07. She's only around 500g (picky eater and has just started eating every week a few months ago) and will not be bred this year even though she is only a few months younger than my other female.