Aging profoundly altered immune system composition and function, thereby influencing host defense, disease susceptibility, and immunopathology. To define age-dependent remodeling of peripheral immunity, we performed comprehensive flow cytometric (FACS) analyses in mice across the lifespan. Peripheral blood mononuclear cells (PBMCs) were collected at defined intervals spanning early development through late adulthood (4 to 52 weeks of age). FACS based phenotyping enabled detailed characterization of innate immune populations (e.g., monocytes and neutrophils) as well as adaptive immune compartments, including B and T cell subsets. This longitudinal study aimed to phenotype peripheral immune aging and was directly relevant to human studies that rely on peripheral blood sampling. In addition, it sought to identify novel biomarkers of immune aging. Collectively, this work generated a high-resolution map of peripheral immune aging and provided insights into immune resilience, disease risk, and translational biomarker discovery.