Not sure what you mean here, brother. Being "found with a rifle" was by itself never legit cause to kill someone, AFIAK. If we killed everyone in Iraq who had a rifle, for example, just about all of the adult male population would have been wiped out. If you're meaning combatants, then combatants are combatants.
One of Bin Laden's wives got snuffed during his raid because she raised up, and
there was a teenager who got shot up pretty badly in Afghanistan and then landed in Gitmo for a number of years because he wanted to throw grenades at US troops.
I've spent a lot of time in the Army and don't recall ROE that said "you can't shoot kids or women, even if they're combatants." Was your experience different?