The adolescent period is a proven fact that happens with all dogs, more-or-less. Comparing it to the "terrible twos" of children desn't even come close to describing it. It's much more akin to a rebellious, unmindful and disobedient teenager in the house.Is there a generally agreed upon time frame in which a pup reaches it's "terrible twos"???
In my mind, I would think that would be when a pup is large and athletic enough and independent enough to get into real trouble... combined with tons of energy.
Not being a puppy-guy, I don't know. Having a puppy, now, I wondering when I will see the worst that my dog will ever be!
A dog's adolescence is the time when everything starts to fall apart, unless you make a concerted effort to see it through to the stability of adulthood. Your dog's adolescence is a critical time. If you ignore your dog's education during that period, you will soon find yourself living with an ill-mannered, under-socialized, hyperactive animal.
it is also, unfortunately, the period when a lot of dogs are abandoned or surrendered to shelters by owners who weren't prepared for it.
All dogs go through it, but the onset, duration and intensity of it varies considerably among individual dogs. Certain breeds are notable for it and if you have a puppy of one of those, it's best to be well prepared. OTOH, some breeds are notable for passing through it almost unnoticably. But again, it is a very individual.
With mixed breed dogs, it's even more individual.
Generally, the period can be thought of as between six months and two years of age, but this is just a very, very general rule of thumb. Better is to watch how your puppy is behaving and take it from there.
The best way to handle it, IMO, is to "train through" it. That means to establish some sort of daily work routine beforehand - when your puppy is still young - and stick to it even when things seem to be going in the wrong direction. Too many people finish up their training at the puppy stage and don't push on through as their dog matures. Try to find an activity that you both like and use that to establish yout training goals. It could be a formally defined dog sport or event, or it can be a more informally defined activity, or it could be something that just you and your dog do. The important thing is to do it together and keep at it.
Here is a good article on the subject:
Adolescence: The Teenage Dog
Look around on the net and you will find a lot of material on how you and your dog can get through this in a positive way.