Depends on the type of cat. If they are a large breed like a maine coon or ragdoll, you would keep them on kitten food longer. If they are small like an oriental/rex type, you would stop sooner.
For my rexes I did not give them kitten food after 4 1/2 - 5 months old - cause they would gain weight really fast if allowed to eat kitten food - it depended on their overall size as to when I stopped.
Charlie was on kitten food up till 5 - 5 1/2 months old (when I ran out of the RC Kitten) - so he was put on adult RC after that and he's fine - growing big naturally.
If some of the breeds (like a rex who only weighs 6-7 lbs tops) was on kitten food for the "recommended" 1 yr as on the package, he would weigh 15 lbs! And be a barrel - not a greyhound.....