If you used to be the bully, owning it to the person you hurt takes more courage than anything you did back then.

Growing out of something is not the same as putting it right, and the gap between those two is uncomfortable to stand in. Going back takes more than the original behaviour ever did, because now there is nothing to gain and nobody watching approvingly. The point is not to be forgiven or to feel lighter. It is to hand the other person a true account of what happened, which they may have been carrying alone.

If you do it, keep it short and make no requests. Name what you did, say it was wrong, and leave the response entirely to them.