According to "The Daily Puppy," puppies are fully grown between the ages of 1 and 2 years, depending on the breed. Smaller breeds mature more quickly than larger breeds.
Depending on the breed, puppies reach adolescence between six and 18 months after birth. During this period, the puppy matures sexually, sheds his puppy coat in favor of his adult coat and almost reaches his full size. After adolescence, the dog's bones reach their full growth. The animal spends the next month or two filling out the muscles and fat on his body until he is a fully grown adult dog.