When to become Concerned

BBS!

My son is 4 months and a week. He had great muscle control from the start, so much so that the pediatrician told me to watch him closely bc he would be an early roller. However, he still hasn't rolled. During tummy time he just lifts his head up and looks around. He hates to be on his back except in his crib and while he'll kick his feet he just doesn't seem concerned about rolling. I really thought by 4 months he'd roll in one direction. I'm not concerned yet, but I think I might be by 5 months. Anyone else have a late roller???