While the story, acting, and general production quality is great, it is not appropriate for anyone under 16 or 17, in general. At least I personally don't believe anyone under that age should watch it. It's gory, yes, but worse for its sexuality.
To be honest with you I never finished the movie (I believe myself to be too young to watch it and stepped out before it was over), but the gore was not what bothered me. There are several sex scenes which are all very graphic, including naked women and a woman briefly shown fully naked from the side midst intercourse as she lays on a table. There is an intense romance between the two male and female main characters which includes at least one very revolting standing sex scene. There is a lot about prostitution.
An abortion is mentioned, there are some torture acts, and the aforementioned gore. Many swear words, including n-gg-r, but that one might not be so offensive because in the setting of the movie it was not so much of a swear word.
I do not recommend it to anyone below 15, and then only if they can block out a lot of sexually related things.
Otherwise, it's an alright movie, from the first 2/3 that I watched.