Alex never experienced life before the Kaiju, and had his most intimate experience with them at the age of 5. Olympia, Washington was a quiet enough place to grow up, and the beach camp grounds outside of the national park were the last place any of them had expected a monster to come crawling out of. It was chaos, and more blood and destruction than Alexander had ever seen, and pure chance that he's wasn't initially among them. Rather than run, he tried to attack the thing, and would have been been killed right then if not for the well timed intervention of Arachnid Fury.
Nick would later adopt Alex, who has adapted well to life in whichever shatterdome is their home, and hopes to be a ranger when he's old enough. He gets his nose into everything and wants to know everything and everyone on base.