Not all dogs start the same and not all dogs train the same. I would find out how the owner of the bloodlines trains his dogs and at what age he expects the dogs to turn on. There are just some lines that start sooner than others. Terriers on a whole start at a much younger age than other breeds so comparing the progression of pups from different breeds is like comparing apples to oranges they just ain't the same.
x2...seems to me that the smaller the breed the sooner they start if they are going to start...and like doggie is saying different breeds and even different strains within a breed start at different ages...same with different pups within a litter especially if they are not line bred...I like pups that show me something along the way...a line of progression. if I don't see it I just might not keep the pup...I am always looking for breeding improvement...I do not keep many dogs anymore but the ones I keep must be worthy of hunting and breeding...sometimes I keep a good hunting dog but it is not worthy of breeding...and this dog more than likely will be replaced when a replacement steps up...
but these pups are freebies and you can hang on to them a while and see what they do...I like the pen to jump start all pups and even to teach an older dog to gain confidence in shutting down a hog...at least the pen can show me what type of bay dog I have...But the bay pen to me should be used sparingly yet it is an important tool...
you really need to find out at what age that strain of dogs start baying... and this should help you make the decision...