The longer a look is in progress, the more likely a person is to keep looking. About then, it starts leveling off. It then declines during adulthood. By late childhood, TV is pretty understandable. The adult decline may be in part due to declining interest and in part due to increasing ability to understand with less effort.
Males look more than females.
Looking varies with content. Some formal features encourage looks, some discourage. Audio is the most influential in this regard. More comprehensible programming seemed to lead to greater attention. They take all this as supporting the notion that viewers pay attention according to comprehension schemata.