It all depends on the puppy. My last guy barked at 7 mos old at a grocery bag blowing around in the wind. We actually thought he was mute or something. He passed away at 13 last March. My new guy started barking at 7 weeks old, at the mailmail. Sarge's brother was 3 weeks old and barked at my son during a puppy visit. He was then nicknamed "Mouth".