I think it depends on the breed and when they stop growing. Little dogs tend to stop growing earlier then big dogs. It also depends on the activity level. I know a husky breeder that feeds his dogs puppy food all the time for the extra calories while they are pulling sleds.I know this may seem like a real no-brainer, but at what age is a puppy considered an adult dog? Specifically in regards to feeding them. I know that puppies tend to have bigger appitites than adult dogs. Also, does it depend on the breed at all? If so, I have a 15 month old GSD.
Rocky is 17 months old now and seems to have topped out at 75 pounds. His no longer runs around the house and yard like a maniac and doesn't seem to be getting any bigger so I've put him on Orijen adult now instead of the large breed puppy. Both are high protein foods so I don't think it really matters which one he eats.