Some kittens are eating machines, and obviously they are growing so they need plenty of fuel. But if you think he is gaining too much weight you should take him to the vet for a once-over and feeding advice. I assume he's neutered?
My most recent kitten was definitely an eating machine. The vet weighed him at 5 months, and then again a couple of weeks later, and he had put on a kilo

He said if he carried on like that he would be diabetic by the time he was a year old, told me to stop using kitten food and go onto adult, and try to rein in the amount he got - every time I walked into the kitchen he was there yelling for food. (Fortunately when he was a year old something seemed to click in his brain, and his appetite diminished so he's quite a slim cat.)
You really don't want to have to deal with problems that come with overweight cats, so if he is hefty, you need to nip it in the bud!