The modern view of the Middle Ages is that life was brutal and short. It is a common assumption that people in medieval society did not know and did not invest much importance in knowing their age. Medieval society also used chronological age as a way to control the development of the person, regulating his or her full entry into society. Chronological age was merely one way of signifying age, and only one indicator of a person's capabilities. In modern theories of ageing individuals may be described in terms of having a physiological age, a social or cultural age, or a functional age. This chapter shows that age theory and classification were found in a wide range of late medieval writings. Medieval society was not interested in doing was testing theory by gathering and using statistics to calculate birth rates, mortality rates and life expectancy.