Obviously, it's totally up to parental choice.
I, for example, am very lenient regarding that kind of stuff - I grew up watching wholly inappropriate media etc.
But, to be clear, the game is an 18 in Europe; it deals with multiple adult themes and has clear adult content like: violence, sex, drugs, racism, rape, alcohol, smoking, gambling, torture, murder, crime, swearing, slavery, prostitution, guns, knives, and the such like.
I would imagine most parents wouldn't approve of this material for non-adults, especially non-teens.