The theory is that by the time they turn 1 babies should be getting a lot of their nutrition from foods with milk being a supplement. By the time all mine were 1 they were only having 2 bottles a day - morning and bedtime so changed them over from formula. If your little one has milk protein intolerance then changing to soy milk should work the same as changing to cows milk. You just may want to check and make sure you are offering calcium rich foods which is hard with milk protein intolerance (one of my twins has the same issue).