Over the years I have bred plenty of old studs and bitches the oldest stud was13 bred to a 12-year-old bitch she gave me a full litter. Over the years well known dogmen would call and tell me that their brood dog missed her last two breedings and would ask if they could send them to me and let me try and get them bred one that comes to mind would be Garret’s Flossie she was sent to me at 10 had her on my yard for 3 years she produced every year I had her. One thing that I have learned over the years is to breed older bitches later in their heat cycle by a few days but now I use a blood test kit to take the guesswork out of it. Also a older bitch needs to be in top shape as in walked every day before breeding and during pregnancy I hope this helps you out.