Some recorders automatically classify women and children as civilians. For women, this is generally because it may be culturally unacceptable in the country of conflict for women to take part in hostilities, and so it was highly unlikely that they would ever be combatants. Regarding children, some recorders believe that they should always be counted as civilian because of their age, even if they were recruited as combatants.
Recorders use different definitions of when children became adults: 12, 15, or 18. Rule 135 of the International Committee of the Red Cross’ customary International Humanitarian Law (IHL) study states that all three definitions can be supported. The Convention on the Rights of the Child states 18, unless “under the law applicable to the child, majority is attained earlier”. All three ages are found in rules for the protection of children in the Geneva Conventions and Additional Protocols.
For example: 18 is the limit for pronouncement of the death penalty; 15 for recruitment and participation in hostilities; 12 for arrangements for children to be identified. Rule 135 of the customary IHL study states that the age of 15 is the most commonly used: there is no definitive answer, and national laws use different ages.
DEFINITION AND CATEGORISATION IN CASUALTY RECORDING, p. 21