Generally, small breeds reach sexual maturity at around 6-9 months of age, while larger breeds may take up to 18-24 months to fully mature.
It is usually best to wait until a dog is at least 2 years old before breeding them, as this allows them time to fully develop both physically and mentally.
Additionally, it is important to consider the health and genetics of both the male and female dogs before breeding them, as certain genetic conditions can be passed down to offspring.