Hooray!
Well, I guess that depends on the 13 year old and your views on various issues. I would have read it at 13, but also I read Shogun when I was 14, so I didn't read much in the way of YA. There's battles where lots of people die but nothing too gruesome ...well, some people get their heads cut off, but I don't describe a whole lot of gory detail. There's (gay) sex scenes that fade to black and are implied but not described ...I'm gay but asexual, so asking me to describe a sex scene is like ...I don't know... expecting me to describe skydiving. I don't do that, either. XD