From the 8th edition of Rabbit Production: small breeds can be bred as early as 4 months of age, medium breeds 4 1/2 to5 1/2 months and large breeds at 6-7 months of age.
However, this breeding schedule is far more common:
small breeds: 5-6 months
medium breeds: 6 1/2 - 7 months
giant breeds: 8-9 months
I breed faster maturingrabbits a little earlier and slower maturing, smallrabbits a little later. Waiting too long can result in a lot of fat building up around the reproductive organs. Too early may result in miscarriage and may stunt the does growth.
I beleive it is the same for both bucks and does -- when I've used very young bucks, the does often did not take or they miscarried.
Pam