FYI: if you want people to know who you're speaking to, quote the post you're replying to when you reply.I assume that if a 15 year old Nazi Soldier with his K-98 rifle killed a Canadian soldier, be would be forgiven based on your criteria.
A soldier in one army killing a soldier of an opposing army in the course of a war isn't generally considered a crime even if the soldier doing the killing was an adult. There have to be extenuating circumstances present before it's considered a war crime.
... which is another bizarre bit about the Khadr story: I still don't see how what he did was a crime at all.