i would make sure you are there for the birth. I have bred full sized does at three years and they seem to have more problems then a one or two year old. But like Stacey said six and seven year i would be really concerned. As long as you get her bred this year i would think she should be alright.
Guinea pigs you have to breed by six months, because their little hips will fuse. Do you have guinea pigs Sarah? thats what got me started in 4-H i had them for many years, had a whole lot of them at one point, used to breed and show TS/W american and american satins REO silkie satins and broken peruvians. My last sow who was a pet just died a few months ago. Maybe someday i will get another, they are great little pets.