The adolescent period of a dog typically begins around six months of age, and will be over when a dog reaches physical maturity say; around two to three years old. The most pronounced behavioral issues will be noticed between six to twelve months old.
Socializing your dog during its adolescent years is critical; even if you’ve just adopted an adolescent dog and his socializing history is unknown, it’s important to continue to carefully expose your dog to different places, people, other dogs, and different situations (like riding in a car) while associating these events with something positive.
You might notice that your dog may quite suddenly appear wary or even fearful of things or situations that he previously had no issue with, for example: he might decide that new people or dogs (or trees, or shadows) should be barked at. This is normal. These moments will come and go several times during adolescence and may last anywhere from a couple of days to a few weeks.
Don’t worry, handle these moments with calm, patience and love, and understand that your dog isn’t always able to control his emotions during these phases. Don’t push or force him to “confront his fear,” and don’t scold him for what may look like rude behavior. Give him time to process whatever spooked him. If he wants to turn away and avoid the scary thing, that’s fine. If he barks at it, that’s fine, too. Often, just crouching next to him and talking with a gentle voice is enough to calm the barking.
Some people opt to “lay low” when they notice their dog is experiencing a fearful phase by avoiding situations that cause their dog stress, like busy streets or large crowds. When their dog shows signs he’s feeling more confident, activities resume as normal. I hope this helps.