Honestly I would say one more season for the female and any number for the male. As long as the female is laying eggs naturally, there is no problem with it. I had a female who was 7 and since she was 5 would lay infertile clutches because she wasn't being bred. But I kept putting her in with boy after year 6 around the time she layed the years before, why have her go through all that stress for infertile eggs? It is harder on them anyway if they don't get fertilized so that is what I do. But I still make sure she lays one clutch on her own that is infertile to make sure she is still laying naturally, if and when she stops producing is when she stops breeding. She is 8.5 years old now and still going strong in all aspects of life.
Phil