I cannot believe that the show has no marks for positive messages and only has one mark for positive role models. The main character, Dr. Gregory House is a person that tends to be a selfish jerk; HOWEVER, he's a good person and he's absolutely brilliant. It's shown that he makes bad, stupid, and dangerous decisions at times, and that he tends to only think about himself, but anybody that watches the show all the way through will realize that he is, in fact, a good person. Regardless, he's also a genius that handles things through logic, which makes him have some very good opinions. In my opinion, he's a good role model himself, but that's not even mentioning the other characters. A great thing about this show is that it's very realistic in showing that everybody has flaws, so no character is a perfect person; however, it's seen that some are better than others. If you take Dr. Wilson (House's best friend), you'll see a prime example of a character that's a great person (while he has flaws, he is genuinely a good person that tries to live morally, even though House is my favorite character to regard as a role model). Outside of characters, the show conquers a huge amount of different topics such as religion, morality, dying, lying, etc., and includes a lot of different opinions. Any show that's well done is going to have characters with flaws and characters that bring bad messages, but I can't believe that people here seem to think that there are no positive role models or messages in the show, because there definitely are!
As for what age the show is appropriate for, I would say that it's appropriate for teens that are fourteen/fifteen. The language features in the show isn't bad; there's not much language worse than what would be featured in something rated PG ("Damn," "ass," etc.). There's a fair amount of drinking, drugs, and sex (both actual sexual themes and plenty of sexual jokes/innuendos). The show also features plenty of depressing themes about death and mortality; combining these themes with the sexual ones, I probably would not recommend the show to somebody that's younger than 14.