Adult food has less nutrients than what puppy food does and puppies need those extra nutrients to develop and grow. I recommend you maybe give him some tough love. Your puppy might be trying his luck in order to getting what he wants so perhaps give him nothing but the puppy food he'll have no choice but to eat the correct food because puppy's are food fiends! They should make the transaction from puppy to adult food at roughly 12 months- for small dogs and roughly 24 months for larger breeds.
We changed our 6month LH pup over to adult at 6months of age, she was on fish4puppies but never really liked it so we have swapped her over to raw and Orijen adult food.
We have recently changed our LH from Fish4puppies to Fish4dogs adult food, he is nearly 8 months. I usually keep the GSDs on puppy food until they are around 12 months but no longer, as CC says some of the puppy feeds have imho far too high a protein level. As long as it is a decent quality adult food our pup should be fine.