In dogs, adolescence begins at sexual maturity, around 5 to 6 months of age. At this age your dog begins to have a sense of self and independence. Your adolescent will become less interested in you and more interested in the environment. He develops an opinion and may begin to question your rules and talk back. By the time your dog reaches 7 to 9 months he is very much like a 16 year old, wanting a later curfew and the keys to the car! The adolescent dog, like the adolescent human, has an immature brain in a body that’s nearly the size of an adult. While adolescence in dogs may last up to two years, the most trying period is from 8 to 18 months of age. This is the age most dogs are surrendered to shelters.