My personal definition of Health: Health is a state that varies among individuals based on a variety of factors including and individuals fitness, lack of disease, genetic disposition, and other illness and disease preventing factors.
My personal definition of Illness: Illness is a state which can be determined both physically and mentally by an individual and outside factors. Illness is controlled by both the environment and society as well as conditions which affect an individuals health.
These definitions have come to me from a variety of sources, the first and foremost of which is most likely my work environment (a radiology clinic) which hosts patients who vary in how healthy they are and how they handle disease. I have seen firsthand that many factors influence the extent of illness and the health of patients. Another factor that influences my perception of disease would be my lifestyle, I have grown up distance running and as an adult have been very active in general. I have seen first hand the affects of fitness and positive lifestyles have not only on general health but also in the prevention of illness and disease.
I would not consider old age to be an illness. If anything I would consider old age to be a manifestation of other diseases. Old age in a lot of ways is just a state of mind. I suppose I would say this under the condition that I don’t “perceive” old age to be an illness. Your body does slow down and lose function, but it is a general loss of function and the losses relative to your peers can be controlled by controlling your health to a great extent. High fitness and medical maintenance can prevent many so called symptoms of old age. What can not be prevented are other actual diseases and illnesses which may come about at an older age (Cancer, Alzheimer’s, etc).
I would most certainly consider Influenza to be an illness and a disease. Influenza symptoms are controlled both by the extent of the virus infection as well as how you perceive the symptoms and how society handles the virus. It is guaranteed to change how you are perceived by society while you are under the affects and it is a difficult illness to shake off.