A stretch perhaps.... but legally true. Seventeen year olds should be barred from military service. If we have a universally agreed construct of what constitutes an adult whether it's 16, 18 or 21 - then all adult behaviours like voting, drinking, driving, having sex, joining the military and owning a house shouldn't be available to children. Or if children do them, it should be illegal.
Kyle Rittenhouse doesn't forfeit the right for self defence. That has been granted in the laws of your land, and it has been protected by the jury. Whether or not he was competent or trained to protect others is the question. He wasn't. He was an amateur filling in the space where trained adults should've been. That was brave or stupid depending on your point of view.
My point of view is that if America is happy for children (even if they are 17) to jump into that space, then it has lost some semblance of it's moral compass.