Our trainer told us that it depends on the dog and the breed. With my labs, because of bone structure issues, you don't want them putting on too much mass, so they went off puppy food at 8 months.
Duke is a much smaller, leaner dog and he needs the extra calories from puppy food, so he is still on it at 9 months. I will keep him on puppy food until he's a year old, then make the switch. Though, to be honest, he gets into Roscoe and Cassie's dishes, so he has had his share of adult food. LOL