I guess with the new game coming out this board is going to be saturated with the question "should I allow my kid to play this".
As an avid games player myself, here is what I think is the definitive answer.
The games industry recognises that not all parents have the time and the will to investigate every single game, to every single outcome to establish whether it is suitable for their children.
As a consequence each game is rated by a panel of experts, who are experts in the psychology of children/young adults and the effect the games may have on them. At the end of this process they make a recommendation as to the age restriction of the game, which is helpfully printed on the front of the game and the back cover, along with some idea of things that the game may contain, like violence, sex, bad language etc. So you as a parent do not have to play for hours to discover them.
As a parent you can do one of two things :
a) Follow the advice that the expert gives you.
b) Ignore the advice the expert gives you, and request that some random, unqualified experts give you advice on an internet forum, often on the basis that they "played the last game for weeks when they were 5 and it never did them any harm".
No doubt some people will say that refusing their kids permission to play the game will cause them a lot of hassle. Well that's parenting. No one said it would be easy, and if you actually want to parent your kids sometimes that involves taking some difficult and unpopular decisions.
GTA is a game made by adults, for adults. It is not for children.