Why do cells age? Recent advances show that the cytoplasm is organized into many membrane-less compartments via a process known as phase separation, which ensures spatiotemporal control over diffusion-limited biochemical reactions. Although phase separation is a powerful mechanism to organize biochemical reactions, it comes with the trade-off that it is extremely sensitive to changes in physical-chemical parameters, such as protein concentration, pH, or cellular energy levels. Here, we highlight recent findings showing that age-related neurodegenerative diseases are linked to aberrant phase transitions in neurons. We discuss how these aberrant phase transitions could be tied to a failure to maintain physiological physical-chemical conditions. We generalize this idea to suggest that the process of cellular aging involves a progressive loss of the organization of phase-separated compartments in the cytoplasm.