Rockstein and Sussman (1979) defined senescence as the period of life where the human body weakens and declines in function rather than grows, a period which is of course associated with physical aging. There is much individual and cultural variation in this process, this is a gradual process, and it occurs across all cultures and in all individuals. Cultural perceptions of aging were also noted by Rockstein and Sussman to affect functional abilities as individuals grow older. An acceleration of senescence that occurs due to external factors such as disease, tobacco use, alcohol and drug abuse, poor diet, or physical trauma is known as secondary aging, and for the sake of brevity these factors will not be considered here. As people age there are numerous physical changes that take place that affect functional abilities, some obvious and some not so obvious. There are also cognitive changes that occur as a result of the physical changes associated with aging that can also affect an individual's functional abilities. Sensory system changes beginning in middle age can affect some functional abilities, especially if they are progressive. For example, many people experience more rigidity in the lens of the eye as they get older resulting in presbyopia, myopia or both (farsightedness or nearsightedness). For some this may lead to functional problems with activities such as reading or driving an automobile, but most people can benefit from corrective lenses. The size of the pupil decreases in most people during their late 40's or early 50's resulting in some people having difficulty with night vision or seeing in dimly lit areas (Troll, 1982). This may lead to functional problems at night or in dim light. Nearly 60% of people 65 years of age and older suffer from cataracts and one to three percent suffer from glaucoma, which can affect functional abilities if not treated. There is also a gradual loss of the ability to hear high frequency sounds starting around the late forties, but under normal circumstances this does not seriously impact functional abilities until later in life. Slightly less than 20% of people over the age of 65 have advanced hearing loss (presbycusis) that can affect functional abilities significantly if not corrected. Taste...

For example, Paterson, Jones, and Rice (2010) reviewed the literature on exercise an aging and found that the implementation of vigorous cardiac exercise three times a week for 30 minutes or more (e.g. walking) or being involved in a weight training program reduced the effects of aging substantially on normal functioning in individuals 65 years and older. These same gains were not obtained by elderly individuals performing daily chores such as gardening, housework, or other chores.
The effects of aging on the central nervous system (CNS) are well documented and a majority of studies concentrate on functional deficits associated with CNS age-related changes. One of the most glaring differences between older and younger people repeatedly appearing in empirical research is the observation of a general slowing in reaction times and a decreased speed of mental processing in elderly compared to younger individuals (e.g., Birren, Butler, Greenhouse, Sokoloff, & Yarrow, 1963). When people are younger they are quick or slow to respond depending on the demands of the situation, whereas as they grow older they require increasingly more time to process information under all circumstances. This reduced speed of processing can affect several functional areas according to Birren el al. And other researchers: (1.) It may account for some of the difficulties older individuals display in remembering new information. (2.) Decreased mental processing speed has been observed on intelligence testing and may explain a great deal of the variance in the decline of IQ scores of elderly individuals. (3.) This decline in processing speed may affect confidence and judgment in fast-paced or unfamiliar environments. (4.) Reduced speed of processing…