Kittens should be kept on species specific kitten food until they are a minimum of 1 year old.  Cats are obligate carnivores, failure to feed them a species appropriate diet will result in eye and heart disease, among other issues. 

For best results, follow the directions found here: Feeding Your Cat | Cornell University College of Veterinary Medicine

For addition reading on dietary guidelines: Nutritional Assessment Guidelines (wsava.org)

Ragdolls are docile and laid back in temperament but still need daily exercise and environmental stimulation.  Exercise for Cats: 12 Cat Workouts That Are Fun for Cats | PetMD

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