How old until you expect a pup to bay?

4.5 months is still young, I would give them some time. The running and hiding thing would concern me more than not baying. But I look for dogs with that natural desire to bay anything. Sometimes its the pen. I had a plott that would knock the back out of his dog house to get away from a coon in a cage, but eat a hog or bear up in the woods. Dogs are individuals "not humans" but individual dogs and are all different.
Im sure there have been great dogs turn on at 2-3 yrs old, but ain't no way im feeding one that long to find out.
its a judgement call that only you can make.