When is right age to put bark collar on pup?

Chris, I really believe it is genetic. I started a long time ago with two strains of Plotts, Weems & Swampland (which goes back to Weems). The Weems were super hyper & barked a lot while the Swampland dogs were more laid back. Now all of them barked when they were first put on a chain but the Swampland dogs were easier to break from barking. Even to this day, 30 years or so later, I still get both types. That being said, they can all be broke if you apply the time. I don't have time to listen to 15-20 dogs barking. It would drive me nuts. Life is too short. I go off to bear camps & hear other peoples dog's bark all night. That does not bother me all that much but if I hear mine, I want to know the reason why. It takes a little while but by being persistent anybody can keep their dogs quiet.
If I hear all my dogs fire up, it is because of a south wind & I know they are winding th hog in my running pen. All I do is yell no & they get quiet.
As far as pups running loose, you do not have to let them run loose to have a good dog but it requires a lot more exposure on the part of the owner to get his dogs out . Running loose day in & day out, those pups are using their nose 24/7 & they learn at a much faster rate.