At the 2009 Comic Con Alan Pall made a comment saying that they aimed the show for adults and feel they have been successful.
In terms of it's content numerous sex scenes, violence and nudity etc :P is the audience really adult.
I'm 17 and know plenty of young people who watch the show. Thank goodness for True Blood, I am a Twilight fan but this is a lot more realistic and interesting and complex. Much more satisfying to watch than the Twilight movies. While I don't doubt adults watch true blood, and I mean no disrespect to Pall, I'm curious.
Are the fans here on sidereel mostly adult, or are the tweens and teenagers making an impact? :P