Something I worry about, but haven't seen anyone mention yet, is that a long-after-the-fact apology seems a little self-serving. I'm the one who feels bad, so I'm going to bring something up again hoping that I feel better about the situation afterwards.
There are people I didn't treat very well when I was young. When I think about reaching out to apologize I imagine the interaction ending with me feeling better and them feeling shitty again.
Reading this thread, however, it doesn't look like that's how this usually goes. So, maybe I should rethink it.