After a male dog or cat reaches sexual maturity at six to nine months of age, they are able to breed any time they are exposed to a receptive female. (pmcofedmond.com)
Physical maturity isn't the same as sexual maturity; some dogs reach sexual maturity as early as 8 months old, but that could be well before the dog has finished growing. (dogcare.dailypuppy.com)
Six to 12 months of age is when your dog reaches sexual maturity as they continue to go through adolescence. (smartdogowners.com)