AKC will register litter's by a sire all the way up to 12 years old. It doesn't mean that the male will have a high enough sperm count though. Even young males can have low sperm counts. It is easy enough to check though since bulldogs are bred by artificial insemination anyways.
You may want to ask the vet I am not sure on that one. Is the dog healthy that would be the main question.
I would suggest asking a vet or another breeder of bulldogs . Keep in mind though that often they have to be delivered caesarian due to their large heads.