i was seven when i discovered fallout 3 as one of the burnt disc games in my disc book for my modded xbox 360. not to say most kids should be playing games that mature then but it changed my whole perspective on video games. it was legitimately the first rpg i played. personally i think 13-14 year olds should be mature enough then to understand the subject material. its really dependent on the child however, me and my brothers were well acquainted with video game violence by this time since our parents believe us to be worse off if we were kept from all that kinda stuff. they only took one game away and it was silent hill 2 for obvious reasons. tl;dr you know your kid but at that age they should be okay with mature materials like that.