Aging creates a destructive feedback loop between gut microbiome deterioration and immune system decline. As beneficial short-chain fatty acid (SCFA) producers diminish alongside bile acid and tryptophan-metabolizing bacteria, intestinal barrier integrity weakens and inflammation intensifies. Simultaneously, declining mucosal IgA and immune aging promote further microbial dysbiosis, creating a self-perpetuating cycle of chronic inflammation termed "inflammaging." This gut-immune deterioration represents a fundamental mechanism underlying age-related health decline that extends beyond digestive issues. The microbial metabolites—SCFAs, secondary bile acids, and indole derivatives—serve as critical signaling molecules influencing regulatory T-cell function, tissue repair, and even brain health through the gut-brain axis. This interconnected network suggests aging isn't simply cellular damage accumulation but involves complex ecosystem breakdown. The practical implications are significant: targeted interventions through specific probiotics, postbiotics, or even fecal microbiome transplantation could potentially interrupt this destructive cycle. While this review synthesizes existing knowledge rather than presenting novel data, it crystallizes how microbiome science is reshaping our understanding of aging biology, positioning gut health as a central lever for extending healthspan rather than merely treating digestive symptoms.