Disease is a much abused word, and the boundaries of its varied meanings to different groups shift over time. Most of the well-known failures that occur in organs and other biological systems over the later stages of aging are referred to as diseases, but are in fact better designated as medical conditions. Medical condition is much broader term that clearly covers unpleasant things that happen to everyone, and are thus not abnormal in a given age group.
Why should anyone care about these fine lines in nomenclature? Why is there a perennial debate as to whether or not aging itself is a disease? The answer, as is the case in so many similar matters, involves the intersection of large amounts of money and government regulation of medical development and clinical practice. The FDA, to pick one of the worst and most intrusive of the world's regulatory bodies, only permits development and clinical use of treatments for specific named diseases. FDA bureaucrats have a list in which diseases are enumerated and painstakingly defined. If a medical condition isn't on the list, then the only way to bring potential treatment to customers within the US is to first engage in year after year of political lobbying and funding studies with no certainty of useful application. This certainly has a deadening effect on the ability to raise funds all the back up the chain, and steers allocation of resources for even fundamental research.
Nonetheless, this process grinds on for aspects of aging such as sarcopenia, the progressive loss of muscle mass and strength. Since aging isn't a disease per the FDA, the development community slowly chips away at converting small manifestations of aging into officially named diseases. People who have more of that manifestation than the average are declared diseased, and thus it becomes possible within the regulatory regime to officially start work on ways to treat them. This whole process, something that has been going on for the better part of a lifetime, is an enormous dead weight atop the natural tendency for innovation and competition. Funds are efforts are diverted from the straightest path to producing new treatments into much less effective sidelines, wherein the entire structure of research and its end goals are first and foremost shaped by regulation rather than the needs of patients.
All this being the case, the regulation of commercial clinical services will nonetheless be bypassed relatively quickly and effectively as soon as viable treatments for aging emerge. Look at what happened for stem cell therapies: they were offered everywhere in the world except the most highly regulated regions, and the regulators eventually blinked because the risk to their careers became ever greater they longer they acted as roadblocks. But this is only the case when treatments are available elsewhere, and when the public is very aware of this fact. There are any number of potential treatments that we don't see at all because of the slowing effect that regulation has on research in the wealthiest and most active scientific communities. The public is none the wiser there, and so the harmful effects of regulation continue unabated. How many lines of research languish without progress or move at a snail's pace because of this? Too many to easily count.
All of this goes some way to explain why people care as to why aging or any specific aspect of aging is a disease. It is keyed to money, pace of progress, and efforts to work within the ridiculous systems of medical regulation in wealthier countries.
Here is an open access opinion piece on this topic where I agree and disagree with varied different aspects of the author's viewpoint. The approach to aging and age-related conditions is presently terrible and inefficient, and it must change to focus more on underlying causes and less on patching over the late stage consequences. The nature of this dominant and futile approach to age-related conditions is very driven by regulation, being an extension of the incentives and regulatory barriers discussed above. Yet where this author advises abandoning work on reversing aging, I say double down on research into ways to repair the causes, to reverse the outcomes, and to create real working rejuvenation therapies.
Aging of biological systems occurs in spite of numerous complex pathways of maintenance, repair and defense. There are no gerontogenes which have the specific evolutionary function to cause aging. Although aging is the common cause of all age-related diseases, aging in itself cannot be considered a disease. This understanding of aging as a process should transform our approach towards interventions from developing illusory anti-aging treatments to developing realistic and practical methods for maintaining health throughout the lifespan. Age-induced health problems, for which there are no other clear-cut causative agents, may be better tackled by focusing on health mechanisms and their maintenance, rather than only disease management and treatment. Continuing the disease-oriented research and treatment approaches, as opposed to health-oriented and preventive strategies, are economically, socially and psychologically unsustainable.
One's understanding of biological aging, either as a disease or as a process that increases the chances of the onset of diseases, has serious implications with respect to interventional strategies. If aging is considered as a disease, then, in an ideal condition and in principle, this could be fully treatable, and a disease-free state could be achieved. However, if aging is understood as an emergent phenomenon occurring progressively in each and every individual surviving beyond certain duration of life within the evolutionary framework, then aging cannot be considered as a disease. This latter viewpoint then transforms our approach towards aging interventions from the so-called anti-aging treatments to achieving healthy aging. This also means abandoning enemy-oriented rhetoric, such as the "war against aging", "defeating aging", and "conquering aging" etc. Instead, interventions in aging require a health-oriented approach and the use of a positive language such as maintaining health, achieving healthy aging, and having active aging. Of course, optimal treatment and management of every disease, irrespective of age, is a social and moral imperative. But considering aging as a disease that happens to everybody is an oxymoron.