This is such a bizarre point to harp on. They could've thought Rittenhouse was a minor or just a young man or a full adult or a grandpa or fuckin Buddha for all it matters - the point is that they chased down and tried to assault/murder a person unprovoked in public, and thats not okay.

All I know is that Rittenhouse has never shown any remorse for having killed two people and maimed a third, so as far as I'm concerned he's a violent sociopath with a taste for blood, which makes him extremely dangerous

First, none of us has any idea what his actual reaction is. Maybe behind closed doors he's cackling and plotting to kill again, or maybe he sobs himself to sleep every night, overwhelmed with regret, or anything in between.

Second, Rittenhouse has very publicly and famously shown remorse and emotional distress for what happened, and the near universal left wing response to this was mockery. "Cried like a little bitch" being the most popular analysis.

Third, its not clear how much one should have remorse for defending oneself from unprovoked attacks by psychos.

Fourth, that all aside, your point is still a non sequitur. To take an extreme example, prisoners in the concentration camps sometimes killed guards to escape. But they needed to in self defense, in order to survive, so not showing remorse wouldn't mean they're dangerous, bloodthirsty psychos. Itd just mean they did what had to be done to protect themselves. Rittenhouse’s case is obviously much less extreme.