Puppy Food Bad for Health

I am currently feeding my 5 month old maltese the specialized "puppy" food (e.g. Iams and Nutra Max for puppies). I was wondering if I should continue to feed him the puppy food for until his first year, as the package directs, or should I start mixing the regular adult food with his puppy food now. I am curious because I heard that you shouldn't feed a puppy "puppy" food for more than a few months after he starts eating hard food, because the extra protein and calcium can be too much for a dog to handl e after a puppy stops growing. So my question is, how long should I continue to feed my puppy "puppy" food, or should I stop now?--Connie