No. You don't figure all military age males are combatants.No, I am trying to do the opposite. By taking the point of Israel supporters and giving it to them by granting that all Gaza teen boys are fighters and not children (I DO NOT AGREE) there are still many thousands of "real' children who have been killed. Same could apply to taking away men over ~55-60 years old and so on from the statistics of Hamas terrorists who have been killed.
Again, this is still giving ground to Israel in their assertion that all adult males killed and crippled were Hamas. Which is absurd.
Rather, you figure casualties amongst those who are obviously not combatants is representative of the civilian death rate. Adjust for demographics and you can figure out the expected civilian death rate of military age males. Those casualties of military age males above this number are figured to be combatants or quasi-combatants. (And note that this will undercount quasi-combatants because some of those were civilians directed into danger.)