Kyle Rittenhouse has been charged with murder.

I believe that the facts of the incident are not in dispute, because of ample video evidence: Rittenhouse was attacked, tried to escape, and when he couldn't escape, he used his rifle on the attackers. However, he is a minor and was therefore in possession of a firearm potentially illegally(1). Does this latter fact make it impossible for him to claim self-defense?

(1) It appears that that section would apply only if his rifle was short-barrel, which AR-15 presumably is not