My vet said anytime after 6 months when they stop growing. Rowdy stopped growing at about 6-7 months, but I waited till I was sure and changed at 8 months. I was anxious to change though, because I was having to feed my old dog Rowdy's puppy food because Rowdy would only eat what the older dog ate - he would not eat his puppy food, if the older dog was getting regular food.
