I believe it is either 8 or 7 months, but I personally would wait until the dog is around 1.25-1.5 years of age to see how he matured and be sure to have all tests and evaluations completed to see if he is worthy of breeding. This is where showing your dogs is a great way to get evalutations. I would also only breed to my own dogs to see what he produced first.
Anyone that on purpose breeds a pup under 1 year of age shows they do not know what they are doing or doesn't know or care about the breed. JMO
Just thought I would add this for more information for you. I am glad you asked. Good job researching!
T.