There are some seriously intense scenes, some extremely violent/graphic, some extremely sexual, (even going so far to show implied sex scenes), and some extremely deep emotional moments and choices. I have watched some children that might be able to handle this at a younger age, (14-15), but the influences are too strong, in my opinion, for anyone younger than 16-17, (really, 18) to watch by themselves.
Several characters are alcohol dependant, and there are many religious themes running through the later seasons. This is important, especially if you are trying to raise your child in faith. There are moments in the show that may cause them to question or doubt, and should only be watched if you are prepared to have conversation with them about the subjects.