For females it's 5-6 months for their first litter and they should be retired at 1 year old, which usually gives 2 litters but some people manage to get 3 on rare occasions if the female is still in good condition. But the females health is the main priority so I believe 1 litter is best.
For males, I'd say breed them from 1.5 years of age, so you can see how their health is up until that time to see if they're good for breeding purposes. Some people do breed from males at early ages, but I think it's better to see how their health is for a long time before you add their genes to your lines to be extra careful
I'm not sure of the retirement age is for males, someone else will have to answer you on that.