I love roosters and I've had a lot of different breeds of them. I've found that Leghorns do have a tendency to be more aggressive than other breeds but every rooster is different. I've have a couple of Leghorn roosters that were wonderful and easy keepers. But I've had a few that became supper. You just don't know about them until they mature. Give them a while to get used to their male hormones when they start to develop at around 4 months. If they show a lot of aggressive behavior at 6 months then they should be taken out of the flock. Just be prepared for whatever happens and don't make a pet of him.