I had some first time mothers in my last rotation one was a year (blue), who i hadnt breed because i was having trouble finding a buck for, and two where 7 month old sisters. I also tried an expeariment with how many visits the does seen the buck. The one year old doe seen the buck once for a while where they copulated 7-10 times and was not returned, One of my biggest rabbits seen a another new buck where the 5 month old buck had a hard time and only connected once with a scream(first screamer) and the next day my last 7 month old went to see the first buck twice once in the morning and once in the evening.
So, the one connect yeilded no litter (will be breed with bigger buck). The one year old nested early and produced two kits ( one being a blue charlie =D). The last 7 month old had a litter of 7 seven( so ill be praticing with a double visit from now on.) I fostered out 3 of her kits to the doe with two as she is far superior mother see is feeding them twice a day and the kits are litterly twice the size even the foster kits now, I will keep her even if her litter size doesnt grow because of how well she foster kits and breed with some of my doe who have bigger litters. So you can take what you want from that.
I think it has to do with gentics im happy with my original breeding stock as they where raised by guys who where heavy on the culling for size and who would also cull bad behavior like bad mothers. I also breed for temperment along with size and color . just something to keep in mind.