Age limits to novels

I have been writing a novel thus titled:  Lazuel:  Dark Beginnings, for about 4 years, however, I have not touched it for 3 of those years due to university taking up most of my time.    This has, I have found, caused me to forget most of the ideas I had when I started writing it, which I find rather irksome and disappointing.

The story is a horror/fantasy, based on a character named Lazuel who is a vampire but I have done away with 90% of the stereotypical stuff and created my own using fantasy as the basis.  The problem I am having is what "Age Limit" I should put this novel in; I know, for certain, it is NOT for children; age 5 - 13, but I am also wondering about young teenagers; age 13 - 16.  In some scenes in the novel it is rather gruesome and, quite frankly, the imagery I have used makes this more vivid.  For example read a phrase taken from the novel below:

"Suddenly, Lazuel begun to feel his internal organs fall away and on to the ground with a light, wet thump; his eyes seemed to be sliding out of their sockets, his intestines tumbled out of him like unfolding chains, his lungs, liver and heart fell to the floor like sliding snow on top of a steep hill....."

In some scenes taboo is used but I try not to use it too much. Should only 18+ read this kind of thing?