You know, with all said and with experience with the underground fence, I am now at a crossroad with age related training. Because:
Daisy (5 mos old) just got her collar. She is doing AMAZINGLY well! Way better than Duke at same age - (surely personality and mix difference). BUT . . . She hears that beeper and comes right back to Mom/Dad/Son with PRAISE. We intentionally made her have a low frequency shock as per training guideline. Once she hears that beep, it seems to be the only learning curve versus Dukes. What a girl!! Duke was the same age when we got the fence 1 year ago except Duke (my little nut) tested it soooo many times his battery went low way to early.
Now however, Duke is MOST respectful of his boundry lines. So wouldn't you think that the younger they are trained the best scenario/outcome with this feisty little breed? Granted, mine are mixes, but age related training may play a big factor in success.