The process of dividing the members of a society into groups according to their ages, applying labels to these groups (infants, teenagers, senior citizens, etc.) and expecting the members of each group to behave in certain characteristic (or NORMAL) ways.
This process is perhaps most clearly observed when people do not behave in the manner expected of them. For example, a child in solemn mood may be described as a 'little old man', or a middle-aged person whooping it up may be having a 'second childhood'. Age-grading is found in all societies, though the gradations and the expectations of behaviour that accompany them vary enormously.