Young men are being radicalized to be extremely violent on the internet. Especially young straight white men (although young men of color and young gay men have been known to fall prey as well). This one looks like a Fuentes follower, part of the so-called Groyper wars. Anyone who's been paying attention could've told you Fuentes is going to get people killed.
The only thing that surprises me about how young he is, is that it was one HELL of a shot. But you can see on his mother's social media that he was raised to use these kinds of rifles from a young age. I just had the misfortune of seeing the close-up footage of the shooting (I do not recommend it, and this is coming from someone who most certainly is not mourning Kirk. I'm sorry for his kids. That's about it). I've never actually seen someone's artery get severed like that irl :/ It was like all the blood just...fell out of his body.