I still encounter people who think that training for a dog should begin at 6 months old. That may have been the case years and years ago when old-fashioned training methods of collar corrections and harsher techniques were popular, due to the physical (and I’d also argue, psychological) risk it posed to the dog. However, it certainly is not the case these days. With modern positive, dog-friendly methods, puppy training can start as early as when your dog is 8 weeks old and just coming into your home. If you have access to your puppy even earlier when they are still with the litter, you can even start before 8 weeks.
Below is a video of a puppy client that I have been working with for months. Broca is a Boston Terrier. We started his schooling at 7.5 weeks old when he came to his new family in Brooklyn. He is almost five months now. His vocabulary is impressive and we continue to add to his repertoire every day.