Boston Terrier is small breed and female can get her first heat cycle 4-8 months of age. But breeding after first heat cycle is not recommended by the vets because dogs at this age are not physically mature and some breeding fitness tests are possible only at the age of 2 years. So, ideally, Boston terrier should be of 2 years of age for breeding. Remember, due to size of head, this breed is more prone to have C-section.