A war crime is an act that is committed in war that violates international acts and/or treaties that bind the rules of war and international human rights.Actions which violate local laws and customs that are committed throughout and as part of a war would also be considered war crimes. The head of countries and organizations who commit the crimes and the main players are tried in international courts when they are caught and sentenced accordingly in most cases. In some cases, the dictator or warlord is returned.
There are cases that come up in modern day where people who were in the military in countries where atrocities occurred are caught and held responsible for the actions of the entire system they were a part of and are charged with war crimes. There is no age limit for a person to be convicted of such a crime and no statute of limitations.