My kitty eats all the time, I mean he will eat a whole dish (dry food only) and I refill it and he eats that. Is it healthy to keep food in the dish at all times for kittens? He is about 3 1/2 months old.
Kittens do need food available as they burn a lot of energy, but if the kittens has not been to the vet to be wormed and start vaccinations now would be a good time. If the kitten has worms it would eat more than usual and not get the nourishment it needs because the parasites take it away from the kit.
I agree with Tru that your kitten could have parasites ("worms"). Unfortunately, that's not an unusual problem for kittens. Make sure to take him to the vet, along with a stool sample to be analyzed for parasites. DON'T use over-the-counter worming products - they're dangerous.
You should also consider feeding your kitten a good quality canned food. It provides better nourishment and is a healthier diet than exclusively dry food since it's closer to what a cat would eat naturally.