There are a lot of dumb things that teenagers do. When I was 16, I was obsessed with listening to and hanging out in the communities of these horrible prank callers who would convince people to break out hotel windows, and would usually yell racial slurs at them in a very aggressive way when they realized that they had been pranked into doing something horrible. At the time, I was extremely depressed, and justified listening to that stuff as well as using horrible slurs as "just trying to get a rise out of people by using the most upsetting words", something I could have only done with the immense privilege I had been afforded as a white person who didn't have to think about how things that I said and did made other people feel because I had no frame of reference for how awful they could be. I now find it completely unthinkable to listen to that kind of stuff, or to have used racial slurs at all, but being around people like that online made me think it was okay and even normal Internet behavior. The Internet was a pretty bad place back then, and to be honest, still is.
I'm not trying to defend it as it is still terrible, but I think a bit more nuance is needed when you're talking about things people do at that age, and there have been many opportunities for him to grow up and realize that what he did was wrong and inexcusable. People have to be given room to grow up and realize that they're wrong. People grow up in different circumstances, different environments, and sometimes they're also surrounded by shitty people who tell them that it's okay to do monstrous things. I don't like the way that people are pretending here as if they were entirely above ever doing anything horrific at that type of age. I don't know about y'all, but when I was 16, I was pretty lacking in empathy and introspection, and finding other groups online of people who were similarly lacking in empathy and introspection led me down a pretty dark path that I didn't really understand the darkness of until I had distanced myself from that stuff and learned a lot of things that I hadn't known before. This is just personal, but I don't really hold people to task for things that they did prior to 21 at this point, because I've known a lot of people who didn't really "grow up" until well after. I don't really talk to anyone who I knew from that time in my life, but the few that I have run into over the years who also listened to the same prank callers almost all express extreme regret and frustration with their ignorance at the time.
Now that I've learned a lot more, I can look back on that period as a bunch of weird adults I was hanging out with online trying to radicalize me into insane right-wing ideology by normalizing it through making me think that it was just "edgy humor". It really freaks me out, because they legitimately had me thinking dumb things like that the words I was using were "just offensive words", but also they absolutely played on me being a bullied teenager who wanted a way to lash back out at people.
What is more concerning to me is that he's pretending that it didn't happen. He should own his mistake and take the opportunity to properly apologize for it, not try to scuttle it. That kind of reaction makes me wonder if he still holds these kinds of views, because I think someone who said or did bad things but had honestly changed would take the chance to clarify that.