JT, many of the intense meat breeders will breed back right away after she kindles. Many breed back 30 days later, so you get 6 litters a year. (30 day gestation, 30 days to feed the kits)
Like every other mammal, the doe is born with a certain number of eggs in her. She will ovulate after being bred, so unlike most mammals, she won't shed eggs once a month.
A doe who is bred back continuously will have a shorter fertile life (in general) than a similar doe who is bred back less frequently. The rabbit CAN live 8 years or so...although I keep hearing that 5 years is a good long life as a "mom".
bucks, like other male animals, can go on until they die. It's quite possible, however, for one to go sterile later in life due to all kinds of problems...again, rather like other animals.