"By that logic...". No, I'm not debating logic with you. That's just the law. Just like you if you say "I'm 18 and old enough to die for my country. Well by that logic I can buy a beer". The cashier is still not gonna sell it because it's the law, and not a ethical debate.
But ya maybe someone in that situation could claim self defense. Here's the impasse I get to with everyone. What did Kyle Rittenhouse do to Joseph Rosenbaum to antagonize or attack him? Not a guess, not what did he do to other people (that we don't even know if Rosenbaum was aware of)...a witness account of what he did to Rosenbaum. We can't just make up a story to fit the narrative we want.