Ive been researching the internet Ive found out the best age to breed is 8-12 weeks, but i cant find any information on the the latest age for first pregnancy... do they have a age were the pelvic bones fuse if they haven't had a litter like guinea pigs ?
The best time for a first breeding (litter 3 weeks later approx of course) is 10-14 weeks - 10 weeks only applies to certain varieties. I believe it is recommended that a first litter should be had by 6 months old, though the closer to the younger end of the breeding scale the litter is had the better quality the babies will probably be.
No I think that is just with Gpigs. I think people who show sometimes wait longer than 12 wks but I think at 1 yr fertility seriously declines if not earlier that said depending on what variety your breeding you may want to breed as early as possible for example yellows that tend to get fat should be bred early because the longer you wait the larger they get and the harder it will be to breed.