Geneva Conventions - Additional Protocols, 1977
Protocol I - International Armed Conflicts
Article 77 Protection of Children....
77.2. The Parties to the conflict shall take all feasible measures in order that children who have not attained the age of fifteen years do not take a direct part in hostilities and, in particular, they shall refrain from recruiting them into their armed forces. In recruiting among those persons who have attained the age of fifteen years but who have not attained the age of eighteen years the Parties to the conflict shall endeavour to give priority to those who are oldest.
77.3. If, in exceptional cases, despite the provisions of paragraph 2, children who have not attained the age of fifteen years take a direct part in hostilities and fall into the power of an adverse Party, they shall continue to benefit from the special protection accorded by this Article, whether or not they are prisoners of war.
Protocol II - Non-International Armed Conflicts
Article 4
4. 3 (c) children who have not attained the age of fifteen years shall neither be recruited in the armed forces or groups nor allowed to take part in hostilities;
(d) the special protection provided by this Article to children who have not attained the age of fifteen years shall remain applicable to them if they take a direct part in hostilities despite the provisions of subparagraph (c) and are captured;
(e) measures shall be taken, if necessary, and whenever possible with the consent of their parents or persons who by law or custom are primarily responsible for their care, to remove children temporarily from the area in which hostilities are taking place to a safer area within the country and ensure that they are accompanied by persons responsible for their safety and well-being.

Problem is that he was 15 whenhe was captured, this is not to mention that there is a total ban on children in war