WWII is something contemporary readers already know a lot about. If our schools are doing their jobs, they know about the invasion of Normandy, the Hitler Youth, the Holocaust, and at least a few of the horrors of the Eastern Front.
I guess whatever maturity is there may be there because I've been keeping a journal forever. In high school my friends would make fun of me - you're doing your man diary again. So I was always trying to translate experience into words.