The canine teeth (the long ones) do not get ground down from eating. Cats actually swallow most of their food whole, with some cracking of hard bits with their back teeth to make them easier to swallow whole. Cats don't have flat molars with with to grind and chew food like people do.
Your cat likely has not grown into his teeth yet. His head will likely grow some more. Similar to how children look like they have such big teeth when their adult teeth first come in, but still have little children heads.