Now, right now. If you already have your dog/puppy, start immediately. Is your dog 8 weeks old? Maybe 8 years? No matter how old they are, start educating them right now. Many people think that there is a specific age that you should start training your dog; but that came from the idea that a puppy had to be large enough to withstand collar yanks. I don't think that any dog should receive collar yanks at any age.
Positive reinforcement training can be used very, very early on tiny puppies. I have taught pups as young as 6 weeks old to sit in a matter of minutes. I have also taught old dogs to sit in minutes as well.
There are of course limits to what we can expect from very young puppies but they can learn for sure. Most of the learning restraints on small puppies are length of time and distractions. Everything is new and their little attention span is short.
That said, every single dog/puppy is different; some puppies have amazing attention spans but we should always remember not to push (mentally) too hard. Training should be fun; dogs should look forward to their training and learning new things. If they don't enjoy it then you are doing something wrong.
Feedback is educating. With simple sounds we can educate our puppies/dogs on things that should be done and should not be done. Starting on the road to learning is in my opinion, essential. Without an education or even learning how to learn, our dogs are quite handicapped in this human world of ours.
Life is all about learning. Everyday brings with it something new. My days are always better when I say to someone "I didn't know that." I love to learn and I love Elsa to learn as well. There is so much to know about this world that we live in. We live with rules and regulations, so to should our dogs.
Education is a gift, give the gift to your dog. Teaching your dog how to maneuver more easily through life is just a win win for everyone involved. So get to it, now.