Male Shih Tzu

Question
How old does the male need to be before he is ready to be a stud?

Answer
The age at which dogs reach sexual maturity depends to a large extent on their breed. Small breeds tend to mature faster than large breeds. On average, however, males become fertile after six months of age and reach full sexual maturity by 12 to 15 months. Healthy stud dogs may remain sexually active and fertile to old age. Adult males are able to mate at any time.Keep in mind that AKC Rules do not allow, except with special documentation, the registration of a litter out of a dam less than 8 months or more than 12 years of age at the time of mating, or by a sire less than 7 months or more than 12 years of age at the time of mating.
http://www.akc.org/breeders/resources/guide_to_breeding_your_dog/step_7.cfm