I can see why. Perhaps the most significant problem associated with aging is centered around our body's replication system. The way that cells duplicate and gr

I can see why. Perhaps the most significant problem associated with aging is centered around our body's replication system. The way that cells duplicate and grow is not perfect. Hosts of environmental, biological, and "pure luck" factors all combine against us in a slow, but inevitable warping of our genetics. In addition to genetic decay, our biological parts get "worn out" over time. Valves close with less force and vessels become inelastic. Our stretchy bits - tendons, ligaments - become scarred with micro-tears over time causing decreased flexibility. Our squishier bits - our inner organs and muscle - tend to become less efficient over time and decay sets in (a rule of thumb is past the age of 30, the average human loses 1% of muscle mass per year). Our squishy-stretchy bits - fascia - tend to lose the fight to gravity as the cells become less and less "sticky" and the skin on our faces droop. As one ages, the mistakes in replication, the decay of our organic bodies begin to add up. As they pile on year after year, the likelihood of getting "sick" increases. Alzheimer's - thought to be brought about by tissue decay and subsequent scarring in the brain. Infarctions (a loss of blood supply, thus a loss of nutrients and oxygen) to a certain part of the body (heart attacks are a common result of cardiac-related infarctions) - can be caused by a stiffening of the walls of blood vessels which lets plaque build up and eventually, when some plaque is dislodged, that plaque might get trapped in a smaller vessel and cause a lethal blockage. Edema (excess fluid building up in tissue) - generally as a result of the weakening of the heart (the heart is a muscle which gets weaker over time) and the decay of the vessels and the muscles surrounding the vessels. And so on and so forth. Fighting old age tends to be thought of as fighting the underlying physical and genetic decay the geriatric (or just aging in general) undergo. Reversing old age, in a similar manner, tends to focus around the prevention or the reversal of that decay. Fighting diseases associated with old age thus is far more limited in scope. While the end result of "fighting old age" might eliminate certain diseases, "fighting diseases associated with old age" will never prevent people from getting old.