I just brought home my new 6 month old kitten Marley on Friday. I also have my 2 year old cat Blue. I am having trouble getting Marley to eat kitten food, he only seems to want the food I give Blue. I just bought a bag of Purina One's Complete Care which is supposed to be for cat's of all ages, so that's what I've been feeding Blue. But I would still like Marley to eat only his kitten food. Is it really necessary for him to only eat kitten food or is adult cat food ok for him?