
The kennel club will register pups from a bitch up to her 8th birthday in the normal course of events, and with special permission past that age.
In countries where there is no upper age limit it is not unusual in some breeds for bitches up to 10 years old to have litters, though I can't imagine a scenario where I would wish to take such a risk.
A lot would depend on the breed as I would not consider a 7 year old bitch to be past her prime in my breed, but a 10 year old I would consider to be starting to get old. In some breeds she would be old.
My Jozi had a litter of 7 last December a month after her 7th birthday and 17 months from her previous litter (she had a litter 22 months prior to that at nearly 4 years of age). she got over that litter and back into condition faster than after the second which was the same number of pups even though the second litter had been a longer gap from the first which had fewer pups.