It has been announced on the Fallen Earth forums that Fallen Earth will be sold with a ESRB rating of "M" for mature. FE Product Manager Circatrix made this statement:
Thought you all should be the first to know that we've received our rating from the ESRB board and we're classified as an M (Mature). You'll start to see this in our ads and videos moving forward.
While this is not all that surprising given the game's concept of a post-apocalyptic struggle for survival, it does pose a bit of a dilemma for the younger audience. Will it effect appeal? Only time will tell!