I think my first question would be what is he attacking. Is it people? A cat, male or female, can be playful their entire life. Neutering or spaying a cat doesn't necessarily take the playfulness out of them. As far as his age, he's old enough to be calmer than he was as a kitten. I'm not sure if there are behavior classes available for cats like there are for dogs. I would be concerned if he is attacking humans rather than playing with them. If I were you, I would speak with the vet about his behavior. The vet may have some helpful suggestions. You definitely don't want your cat to hurt someone. Good Luck!
If the cat is neutered after reaching sexual maturity, it can take longer for the hormones and resulting behavior to be completely out of his system. And he might have been attacking for reasons other than what might have been controlled by hormones. Are there other pets in the house? A new baby? A new significant other? And I hope he's not biting - if so, and he actually breaks the skin, be sure to wash the wound thoroughly and watch for infection. Same with scratches. Cat mouths and cat feet are really dirty -- think about their feet being in the litter box and they lick to wash themselves all over. (And now I think I should wash my hands after petting my cat. Sigh.)