I go by weight, all my males have bred successfully (as in they did the deed - not sure if all took or not) at about 900g.

I have a YB that I hope will be 700g or so come the season, if he seems up to it I may attempt him.

I am just hesitant to breed the younger males, as they get so intense and we want to make sure they have a good weight in case they decide on a 6 month fast following.

Bruce