My cats are eating me out of house & home! Help?

My cats are eating more now then ever! I usually don't need to fill their bowl more than once a day. Now, less than an hour after I've filled the bowl-it's empty again. (They get really hyperactive when the bowl is empty) I have to buy cat food more often than normal. No, they are not gaining weight. I have 2 cats ages 1 and 4. The 1 year old eats much more than the 4 year old. Is it because of a growth spurt for him or something? Do I need to ration the food and/or give them seperate bowls? I don't want to deprive my cats as I am told to keep food & water in their bowl at all times. If I do ration, I don't want to deprive my oldest cat of food-who does not eat nearly as much as the 1 year old. Any suggestions?