At one year old, he should defintely be eating adult food!
It is recommended that you feed puppy food ONLY for the first two months that you have the puppy at home and then switch to adult food. I know that sounds a bit odd, but that is just a rule of thumb, but most people feed puppy food longer than that.
Another good “rule of thumb” is to switch to adult food when the puppy has attained 90% of his growth. This of course varies by breed and size. If you know the average size and weight of a pit bull (height 17-20 in at the withers and up to 65 pounds in weight), then you could figure it out from there. That range is usually within the 7-12 month of age. Of course, each dog grows at a different pace.
The nutritional formulation of puppy foods (especially the extra protein and calcium) can actually cause problems in puppy development, and that is something that you don’t want, though many puppy owners are unaware of the damage that they are causing their puppies by not switching to a high quality adult food at the right times. The problem tends to be with growth of bones versus the growth of tendons, ligaments, and muscle. The growth rates are not the same for each and so the connections betwen them are strained. What this means to your dog is if the dog jumps wrong or is playing too hard, the connections can be torn, resulting in A LOT of pain and potential for numerous problems later on. This typically happens in the front shoulder and requires surgery and several months of confinement to repair. The added calcium in puppy food may also deposit on puppies’ bones causing limping.
It is key that you slowly switch your puppy over to a HIGH QUALITY dog food. Don’t do it immediately, or you will have a gastric upset on your hands and everywhere else!
When I say high quality food, I mean HIGH QUALITY! Do not buy the junk food in grocery stores. The foods are not meant to feed a rat, let alone a dog. The foods contain way to many by-products and fillers (grains and chemical) that can cause harm to your dog.
Best of luck to you and the pup!