Media companies create their content (programming), not for everyone in the world, but for specific people called audiences or target markets. Just like diapers are bought only by new parents, and bubble gum is bought mostly by teens, media wants to reach only specific people in the audience. These target markets are people grouped together by Demographics and/or Psychographics.
Demographics are ways to group people by characteristics that don't change, or change very slowly. These characteristics include gender, age, ethnicity, income, education level, geographic location, etc.
Psychographics are ways to group people by the way they think. This includes, political affiliation, spending habits, religious beliefs, etc.
Do seniors watch cartoons on TV? Yes. Even though the majority of people watching will be children, about 20% or less of the non-targeted audience will also watch. The 80% or more people who do watch are what we call the Ideal Demographic. 80% of the people watching American Idol are teens. 80% of people reading printed newspapers are above the age of 30. 80% of people watching Football on TV are men.
Advertisers like target markets because they can sell their products to the people most likely to buy them. This is why dishwasher soap ads only play during daytime television. It's because 80% of the people watching daytime television are stay-at-home mothers or people otherwise at home during the day.
The next time you see an advertisement on TV, in a magazine, or anywhere else, ask yourself why you saw it. Are you a member of that media's ideal demographic? You probably are.