I've had some that never got aggressive, and one that I needed to get rid of. A silkie lol; my most aggressive roo of all time was a silkie
Springtime. That's when i be had to keep a close eye on the boys, especially if there's only 1. Oddly enough, I've had the best boys when there's a few of them; keeps them preoccupied with each other and not worrying about the hens so much. That's when they can get dangerous; when they're the dominant roo and are protecting their hens. My Blue Andalusian got himself kicked off the farm for pouncing me when I went to grab a hen that was not where I wanted her to be. She squawked and he was immediately on my back. Didn't hurt me and didn't mean to, but its an example of how protective they are over their flock. It was my fault for making his hen squawk! I was due with a new baby and didn't want to have to deal with chicks, so I culled all my roos, otherwise I would still have him; he was my best roo, very good boy. He wasn't scary mean, just protective. That's why little kids are more prone to being "attacked" than we are. They're usually an unfamiliar presence and his job is keeping unfamiliar things away from his ladies.
They can be trained, and letting the kids in with them as much as possible can help, but come springtime, hormones can indeed take over, and they can lose their brains and get overprotective. That's when the training will either save him, or send him to the stew pot. The biggest thing is making sure he knows from day one that he can't rule the humans; they are the real roosters in a sense. I teach my kids to not ever turn your back on a roo, and never move out of his way, make him move for them. They also get to pick him up and thump him on the head and hold him there until he figures out that he has to submit to them, too.
They're unpredictable until you get through the first spring, then they either calm down, or become Sunday dinner; just never know until it happens.