Biomarkers are essential tools for assessing biological age and predicting longevity. Cystatin C, a small protein produced by all nucleated cells, has emerged as a valuable biomarker for kidney function and overall health. Elevated levels of Cystatin C have been linked to a higher risk of age-related diseases and mortality, making it a promising indicator of aging and longevity. Its ability to accurately reflect renal function independent of muscle mass and other factors makes Cystatin C a reliable marker for assessing overall health and predicting lifespan. Incorporating Cystatin C measurements into longevity assessments can provide valuable insights for personalized health and wellness strategies.