ABSTRACT
Introduction Age is an indicator of how long one has lived but is not a complete indicator of a specific individual’s capabilities and limitations. One can easily imagine how a physically fit 55-year-old triathlete could outperform a 34-year-old in a marathon, personified by Cliff Young, the 61-year-old winner of the 1983 Sydney ultramarathon (544 miles). Similarly, with respect to cognitive capacity, there is wide variety in capabilities and limitations that are linked with age. Thus the definition of “old” and “older” can be a tricky issue. The issue is further complicated by the sheer variability in any given ability as we get older. Generally, for younger and middle age groups, capabilities vary, but this variability widens as people get older; the older adult age group (defined as those aged 65 and over) are more different from each other than people in other age groups differ from persons in their own age group.
