I've usually bred between 5 adn 6 months of age, with my dutch, hollands and mini rex. Though I've only ever had two mommy's lose their first litter. One dutch and one holland, all the other have all raised their first litters(Kitty raised them until they were 3 weeks and then killed one, so i removed the other and the foster died). I try not to breed more than 3 times a year per doe. while some i've culled, some to pet homes, others i have sold into show/brood.
My mini rex doe, i bred her at 6 months and she can have one litter a year and still produce the following year at once a year, she usually will take care of young kids if i have to remove them from mommy early even though she has no milk(kits are bottle fed milk but munching on pellets) but her sister was waited until she was almost a year to bred and still, at 3 years of age will not produce live kits, she kills them after a few days if she does produce.