Age affects refers to the changes that occur in the human body and mind as a side-effect of aging. This can be a slowing of reflexes and response times in comparison with younger individuals but does not necessarily refer to an actual decline in mentality. Unfortunately, as people grow older they tend to become less physically and mentally active and tend to compare current performance to when they were younger.
Also, in our society older people are sometimes overmedicated by their physicians and are also subject to depression as a result of loneliness and isolation from family, friends, and productive activity. The latter can frequently be remediated by careful screening of medication and life style changes such as staying engaged and continuing to stimulate the mind.