The timing of entry into “old age” varies greatly among individuals. Often an arbitrary, and probably inappropriate, cut off for being old is set at 65 years (especially by policy makers). The concept of age is multidimensional in nature and the overall age profile of an individual can be constructed from several concepts:
The number of years since a person was born – this is the easiest way to define age age and time are synonymous. Most people assume that chronological age is synonymous with the concept of age, but this is not necessarily relevant to developmental age or a range of social and functional capacities. This is the most pervasive concept of age in society (eg compulsory retirement from employment at age 65 years). Chronological age does allow the use of arbitrary age divisions - eg: Infant (0-2yrs); Child (3-12yrs); Adolescent (13-17yrs); Young adult (18-24yrs); Adult (25-44yrs); Middle age adult (45-64yrs); Young old (65-74yrs); Old (75-84yrs); Old-old (85-99yrs); Oldest-old (100+yrs).
Individuals differ substantially in the way that they age and the rate at which they age, so the biological age is considered an estimate of a persons present position relevant to their potential life span - refers to what an individual can do. It can be viewed as an index of biological health – it can be different (greater or less) from those of a similar chronological age. Determination of biological age will require the measurement of a number of a single parameters or a group of different parameters. This is problematic in that different body systems in different individuals may age at different rates, making a useful universal parameter(s) difficult to obtain. In children, dental and sex development can be used as a measure of biological age.
Considered to be related to the adaptive capacities of an individual – how can they adapt to the changing environmental demands when compared to others of a similar chronological age.
This is considered to be related to the social roles, social participation and expectations that people have on themselves as well as those imposed by other members of society . Many individuals may behave in a fashion that is either younger or older than their chronological age.
The ability to function relative to others of the same chronological age. This can be considered a better predictor than chronological age. Cognitive status and activities of daily living can be measured and compared to that of a chronological age cohort.