For most people, old age is feared because it is associated with disability and disease, and it is true that the prevalence of disease increases decade by decade. However, the ageing process is not the principal cause of disabling disease, and many of the disabling diseases of old age are preventable.
It is true that disease occurs more commonly as we grow older. With every year that passes the probability that a person will develop or be diagnosed as having a disease increases but this does not prove that ageing causes disease. The reason for this increase is the ridiculously simple explanation is that every year that passes means that the person has been exposed for yet another year to the risk factors that cause disease. It is usually the length of exposure to risk, both environmental risk and lifestyle risk, that causes the increase in disease not the ageing process.