This preclinical review examines the role of the NMN transporter and extracellular NAMPT (eNAMPT) enzyme in mammalian aging and longevity, focusing on how NAD+ biosynthesis pathways regulate cellular aging processes. The authors discuss evidence from animal models and in vitro studies demonstrating that efficient NMN transport and eNAMPT activity influence NAD+ availability and may affect age-related physiological decline. This is a review-level analysis synthesizing existing preclinical research rather than reporting new primary experimental findings.