Aging is a central notion in various domains, including biomedicine. There is an urgent need for a unified and interdisciplinary framework for articulating the multifaceted character of aging. To take initial steps towards such a framework, we provide an ontological analysis of the six defining features of aging based on Basic Formal Ontology (BFO): functional decline, structural damage, reserve depletion, cellular senescence, phenotypic change, and the increase in the probability of death or disease. Our proposal leverages the BFO dispositional account of function as well as a BFO-compliant theory of dispositions and dispositional approach to causation. We also briefly discuss premature aging, disease, health, and homeostasis in relation with aging.