Organismal aging is often characterized as a steady, monotonic decline of organ and tissue function. However, recent studies indicate spatial and temporal variations of aging rates across the lifespan. We consider these variations from the perspective of underlying cellular changes. Cells in certain tissues may age earlier and produce signals that accelerate the aging of other cells, locally or distantly, acting as drivers for organismal aging and leading to a lack of synchronous aging between tissues. As cells adopt new homeostatic states, cellular aging can be viewed, at least in part, as a quantal process we refer to as digital aging. Analog declines of tissue function with age may be the sum of underlying digital events. Cellular aging, digital or otherwise, is not uniform across time or space within organisms or between organisms of the same species. Advanced systems-level and single-cell methodologies will refine our understanding of cell and tissue aging, and how these processes integrate to produce the complexities of individual, organismal aging.