Well, different people have different ideas about puppy nutrition. I don't believe in feeding puppy formulas at all - I think they're overloaded in calcium and protein (and too much of any particular vitamin or mineral is as bad or worse than too little). IMO a good quality food is a good quality food whatever the age of the dog.
Of those that do feed puppy food, I think that most switch to adult food by 6 months. A few people keep it up until up to a year old. Really, it comes down to what you feel is best for your puppy.