In high mortality populations, the aged are a very select group: they are those who have survived the dangers of being born, the risks of infancy and childhood, and the sicknesses and accidents of middle age. Until recently, in the countries of Southeast Asia, fewer than 30 per cent of those born could be expected to live to age 60.

Having survived the multiple assaults on their health during childhood and adulthood, what is the health and disability status of those increasing proportions who reach old age? Diagrammatically, the situation might be portrayed as in Figure 6.1.

The proportion of the population enjoying good health gradually declines from age 40 onwards, and the decline accelerates from about 60 onwards. Similarly, the proportion who are neither sick nor disabled declines steadily. It has been argued that, because of medical successes in postponing death but less success in reducing morbidity or disability, the gap between these curves and the mortality curve has widened in recent years, implying an increasing proportion of the elderly population who are in poor health (including an increasing proportion in poor mental health). This is, of course, related to the increasing proportion of the elderly who live to “old-old” age — beyond 75 years — implying an ageing of the aged population itself. (It was noted earlier, however, that in the ASEAN countries over the next two decades, there will not be a universal trend towards an increasing proportion of the very old among the aged population.)

On a more positive note, Fries (1980; 1983) argues a “rectangularization of morbidity, disability, mortality” — related to a steep drop in the mortality curve around age 85, because of a postulated ultimate upper bound on life expectancy determined by biological limits on the normal life span of the human species. Fries' point is that

Strategies for postponing infirmity include preventive approaches to premature chronic diseases, and to changes in prevalent social expectations for the elderly.