You surely have heard about PEGI or ESRB. Age-based rating systems are important in the game industry and they should be taken into consideration by developers. Knowing beforehand that you are developing a game that is supposed to be PEGI 7, for example, already says a lot about the game design itself.
The same goes for mature-rated games.
Sometimes, the very fact that they are mature-rated is part of the concept.
In fact, the idea of including an expected age-based rating in the concept might help in creating a game actually suitable for that age restriction.
There is an everlasting debate about these systems and how they are (or are not) useful to consumers, especially parents choosing a game for their children. As will ...
