One time, while talking with a group of children, I was discussing the Ten Commandments and how we should treat each other with love and respect. A young girl looked at me and said, "I guess this means I can't be a bully any more." She vowed to change. Knowing this girl, I believe she was sincere. She really hadn't thought about the fact that what she was doing was gravely wrong. This was a teachable moment, and she appeared to take the lesson to heart. That's the difference between childhood bullies and adult bullies.
Someone who has been abusing others for decades is very hardened. As an adult, they are much more resistant to change. I'd venture a guess that the longer they've been at it and the older they are, the likelihood of them ever amending their ways decreases to the point where it will take a miracle of sorts to bring them to repentance. As someone else pointed out, they've lived their entire lives without learning a thing. This is the horror of adult bullying.
An adult who hurts others has had many more opportunities to change. They haven't taken them. Plus, they've become much more adept at evading detection. As they continue on their treacherous course, they leave a trail of broken hearts and shattered lives.
Perhaps one of the saddest thing to see are geriatric bullies. As any nursing home director will probably tell you, this is a huge problem. Even senior citizens form cliques, and shun people they don't like. This is a problem that would be comical, if it weren't so sad. It was reported in another publication that anything a nursing home resident does, which elicits envy, can also lead to being shunned. One woman whose niece took her home for a holiday was worried about what would happen when she she returned to her facility. She anticipated being excluded by those who had no family members to take them out.
In one of the articles I read, the nursing home staff had stopped all efforts to change their behavior. By their eighth or ninth decade, these mean women were quite set in their ways.