Dogs are constantly learning animals, whether it’s from their environment, from socializing with people or other animals, or from direct training. But people say the hardest age to train a dog was probably between 5 to 8 months with months 6 and 7 being the worse.
Dogs become “teenagers” and seem to forget everything they have ever been taught. During this time, they’ll often test their owners, seeing what they can get away with.
This period is individual to each dog, but it may last until he’s two years old.