Dogs reach physical and emotional maturity at eighteen to twenty-four months of age. They may look fully grown long before then, but they're still developing, so be patient with their puppy-like enthusiasm and adolescent testing of your authority. As dogs reach maturity, their nutritional and exercise needs change. If they're longhaired, their coat comes into its full glory. Appropriate diet, grooming, dental care, and exercise are all essential to keep your adult dog in peak condition throughout his life.