Do you have other cats? A young male cat will participate in rough play with his peers; if he has no peers he will try to play roughly with you! Direct his play to an acceptable toy with vigorous activity. Something like a stuffed toy on a string and stick, that you can get him “stalking” and “pouncing” on. A cat his age wants periods of intense activity. Withdraw your hands, say “no” firmly, then offer the alternative play. If the behavior persists, consider an appointment with an animal behaviorist or communicator to help alleviate the problem.