Dogs are considered adults from 12-18 months (up to 2 years for giant breeds).
However, this doesn't mean you need to change the food at this point. It is much more important to assess that the puppy has completed key development. Our puppy food has increased levels of protein (for overall development) and calcium and phosphorus (for bone and skeletal development). These are at the optimum level to ensure healthy and steady growth of the puppy.
As all of our foods contain high levels of meat, and naturally occurring calcium and phosphorus; moving over too soon or too late isn't a major disadvantage. Although we recommended waiting until the puppy has achieved a good level of body mass (total size, weight and body fat) and has a positive body score (doesn't look too thin, ribs can be felt through body fat cover).