I know it's a late response, but I think when you switch from puppy to adult food (or if you feed right from the start an all stages food) depends on the needs of the particular dog. Keep in mind puppy food typically has more protein, fat, and calories than adult food. That is the big difference between them generally... though with many of the higher quality foods, you lose that difference, as you'll find with many of them, they have just as many calories, and as much protein and fat (if not more) than your average puppy food.
For me, I make the change when my dogs body tells me it needs to be changed, based on body condition. If they are getting plump at 6 months on puppy food, I'll go ahead and switch them to adult, as it's clear they don't need the higher calories of the puppy food. If they are the type who go out and run, run, run, they may stay on puppy food a long time. I have one that is extremely active, and she at just short of 2.5 years old is still on puppy food. She is hard to keep weight on (and no she isn't wormy, nor does she have coccidia or giardia) due to her activity level, and I would figure her metabolism. I have tried switching her over to adult, and she can not hold her weight. It seems to run in this particular line... I've had several from it now who I've kept on puppy food for a long time because they were hard keepers as young dogs. They all eventually come out of it, though I must admit this one is the latest. Most are on adult food by 12-18 months old.