Whether a type of media is considered to be for the older or for the young is mostly cultural. I consider certain cartoons for all ages. I like watching Yugioh anime but I also like watching horror and sci-fi movies or certain R rated action movies. I even like watching X-Men cartoons online. Also, people who never watched certain cartoons and don't know the story shouldn't say it is for only young people. Something with a storyline is more interesting and grown up than something that has no story. Also, as long as you don't actually buy merchandise about certain things and you only go as far as watching certain things, I wouldn't think it is childish.
I could say The Simpsons is childish because of its so-called boring humor, no story really, poor character art style, and the fact that the characters never age, and that Family Guy is corny and childish and an immoral and sexually obsessive show with an equally crappy art style (my feelings) and that the main character (forgot that man's name) is the prime example of someone that has been extremely polluted by USA culture (the worst parts of it that seem more and more common these days) and therefore has grown obese, stupid, lazy, and has no discipline or good qualities, and is not polite or clean or moral in many ways. What would a spouse ever see in someone like that?
King of the Hill would be more grown up than that because of the art style and the fact that characters can die and age. Same with a lot of Marvel shows. They seem more grown up and have good stories. Anime also can be considered more grown up since characters die and age, the stories are usually great and detailed, and it deals with darkness and light and is usually more serious, especially if you watch the subbed Japanese versions, excluding childish Pokemon, of course. Also, anime has a very cute art style to boot and someone with a soft spot would think it is cute and that wallpaper is cute.
One foolish way of thinking is when people think it has to have detailed and gory violence or sex to be grown up. I hate that stereotype.