When you are asked the question “How old are you?” what crosses your mind? Is it the number of years since the day of your birth? Is it how old you feel at that time? Is it defined more in terms of where you are biologically, psychologically, or socially than in terms of calendar time? You may not have thought about it, but age is not a simple construct (and in the case of people such as the! Kung, it has no meaning at all).

Likewise, aging is not a single process. Rather, it consists of at least three distinct processes: pri­mary, secondary, and tertiary aging (Birren & Cunningham, 1985). Primary aging isnormal, disease – free development during adulthood. Changes in
biological, psychological, sociocultural, or life­cycle processes in primary aging are an inevi­table part of the developmental process; examples include menopause, decline in reaction time, and the loss of family and friends. Most of the infor­mation in this book represents primary aging. Secondary aging is developmental changes that are related to disease, lifestyle, and other environ­mentally induced changes that are not inevitable (e. g., pollution). The progressive loss of intellectual abilities in Alzheimer’s disease and related forms of dementia are examples of secondary aging. Finally, tertiary aging is the rapid losses that occur shortly before death. An example of tertiary aging is a phenomenon known as terminal drop, in which intellectual abilities show a marked decline in the last few years before death.

Everyone does not grow old in the same way. Whereas most people tend to show usual patterns of aging that reflect the typical, or normative, changes with age, other people show highly suc­cessful aging in which few signs of change occur. For example, although most people tend to get chronic diseases as they get older, some people never do. What makes people who age successfully different? At this point, we do not know for sure. It may be a unique combination of genetics, optimal environment, flexibility in dealing with life situa­tions, a strong sense of personal control, and maybe a bit of luck. For our present discussion, the main point to keep in mind is that everyone’s experience of growing old is somewhat different. Although many people develop arthritis, how each person learns to cope is unique.

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When most of us think about age, we usually think of how long we have been around since our birth; this way of defining age is known as chronological age. Chronological age is a shorthand way to index time and organize events and data by using a commonly understood standard: calendar time. Chronological age is not the only shorthand index variable used in adult development and aging. Gender, ethnicity, and socioeconomic status are others. No index variable itself actually causes behavior. In the case of gender, for example, it is not whether a person is male or female per se that determines how long he or she

will live on average but rather the underlying forces, such as hormonal effects, that are the true causes. This point is often forgotten when age is the index variable, perhaps because it is so familiar to us and so widely used. However, age (or time) does not directly cause things to happen, either. Iron left out in the rain will rust, but rust is not caused simply by time. Rather, rust is a time-dependent process involving oxidation in which time is a measure of the rate at which rust is created. Similarly, human behavior is affected by experiences that occur with the passage of time, not by time itself. What we study in adult development and aging is the result of time – or age – dependent processes, not the result of age itself.

Describing a person’s age turns out to be quite complicated. Here’s why. Perceived age refers to the age you think of yourself as. The saying “You’re only as old as you feel” captures perceived age. Where people are, relative to the maximum number of years they could possibly live, is their biological age. Biological age is assessed by measuring the func­tioning of the various vital, or life-limiting, organ systems, such as the cardiovascular system.

Psychological age refers to the functional level of the psychological abilities people use to adapt to changing environmental demands. These abilities include memory, intelligence, feelings, motivation, and other skills that foster and maintain self-esteem and personal control.

Finally, sociocultural age refers to the specific set of roles individuals adopt in relation to other mem­bers of the society and culture to which they belong. Sociocultural age is judged on the basis of many behaviors and habits, such as style of dress, customs, language, and interpersonal style. Sociocultural age is especially important in understanding many of the family and work roles we adopt. When to get married, have children, make career moves, retire, and so on often are influenced by what we think our sociocultural age is. Such decisions also play a role in determining our self-esteem and other aspects of personality. Many of the most damaging stereotypes about aging (e. g., that older people should not have sex) are based on faulty assumptions about sociocultural age.

In sum, a person’s age turns out to be quite com­plex. Think about yourself. You probably have days when even though the calendar says you’re a certain age, your exploits the day before resulted in your feeling much younger at the time and much older the next morning. How “old” anyone is can change from one moment to the next.