Oh yeah it's definitely 18+ IMO. Blood, sex, torture, and I think an occasional use of the c bomb.
Gosh.
Pancho, as a rough guideline, if a program is made by HBO, it will feature explicit sex, bloody murder and probably torture.
GoT is one of the most extreme. Its even mentioned in the wikipedia entry. You have frequent full-frontal nudity, blowjobs, and male/male, female/female and group sex scenes. Decapitations, disembowelments, hands being chopped off - and not in a cartoon-like way, this is blood gore, agony and screaming.