Also they keep saying "he crossed stare lines" why is that such a big deal? Especially if he lived near the state line, surely the issue is how far he went rather than if there happened to be an arbitrary line on the way.
From what I can gather, it makes it a federal crime, which is more of a life sentence if you're sent down. Short version is: his older friend in Wisconsin bought the gun for him because he was underage. Rittenhouse lived in Illinois, so if he'd carried the gun over the state line it would have been a federal crime. (Americans, correct me if I've got this mixed up).
But it's irrelevant now, as the gun was stored in Wisconsin all along, and Illinois didn't prosecute anyway.
The evidence this week suggests it's pretty much self-defence, the guy he shot even admitted he lowered his gun at Rittenhouse, and the state prosecutor threw his face into his hand. On a vaguely related note, this happened to reggae star Nitty Gritty when he drew a gun on Supercat in the US. Supercat shot him and won on self-defence. The other one tried to grab his gun, and the other tried to smack him with a skateboard. The reason nobody's really mourning the two he shot (and that Twitter's been a bit muted on this) is it's emerged one was a convicted child rapist and the other was a complete nut who tried to stab his own family. So he did some good that night.
But I agree with you, he seems an impressionable, immature kid who was desperate for some heroics and ended up in a complete mess. Maybe the book deal will get him a nice house somewhere.