By now, your rookie roo should be demonstrating his individual temperament. If he's a nice guy now, you have good material to work with.
As
@Overo Mare pointed out, his training should begin now by not cuddling and coddling him. Keep the familiarity to a minimum. Lavish your affections on the girls, not him.
Around four or five months, he will begin getting his hormones. This is when there's potential for misunderstandings and mixed messages, and if your cockerel is confused, it can come out in aggressive behavior. Usually that occurs when a chicken keeper has been overly familiar with the little gentleman. It confuses him as to what his role is and what your role is.
Again,
@Overo Mare has a good suggestion. Ignore him. This shows that you trust him to figure out his role in the flock and he should reciprocate by respecting your role. If he gets it wrong, immediately correcting his behavior will let him know he was getting off on the wrong foot. Then ignore him again, even when he makes clumsy attempts at mating a hen. Try not to laugh yourself sick where he can hear you.
Correcting a cockerel is as simple as immobilizing him until he calms down and surrenders, then release him. That's all it takes. Cockerels are fast learners.