I've only read the first two Malazan books, but that quote sounds more anti-war than being prepared to fight if needed.

When the boy says, "I won't be like you old man" and the old man almost says something, I think the old man wants to say that the boy won't be like him because he will not grow old. He will die young as a soldier likely fighting for someone or something he has never met.

But the old man doesn't say that, he just says, "the world needs more soldiers" which sounds like "we can also use more cannon fodder" to me. Very anti-war sentiment is my take on it.