Background: Aging is a biological process that drives metabolic and functional decline across physiological systems, including immune system. Natural killer (NK) cells, key mediators of tumor and viral surveillance, have emerged as a promising immunotherapeutic tool; however, the molecular and metabolic pathways that shape NK-cell function during aging remain poorly defined. We show that expression of Tumor Suppressor Candidate 2 (TUSC2), a mitochondrial protein with structural features consistent with a calcium sensor, steadily declines across multiple human tissues with age. We investigated further how the loss of TUSC2 impacts NK-cell development and the differentiation of distinct functional NK-cell subsets. Methods: Phase 1: Human single-cell RNA-seq data from harmonized datasets of healthy blood NK cells and tissue-resident or tumor-associated NK cells were analyzed. Core functional programs including interleukin signaling, metabolic pathways, and developmental signatures were examined. Differential expressions between TUSC2high and TUSC2low NK cells were assessed and integrated with these programs. Phase 2: Splenocytes were collected from young (1-3 months) and aged (18-21 months) Tusc2 wild-type (WT) and knockout (KO) mice. Single-cell immune suspensions were stained with NK lineage and maturation markers: CD122, CD49b, CD11b, and NKp46 to delineate developmental stages I-IV. Following surface staining, cells were labeled intracellularly to identify transcription factors and functional mediators. Results: TUSC-2 expression strongly correlated with the maturation of NK1C (effector-terminal) population, as well as with cytotoxic and metabolic programs in these functional subsets. NK cells at early developmental stages (I-III) showed comparable frequencies between WT and KO mice, indicating preserved early progenitor commitment. However, absence of Tusc2 generates an inappropriate downregulation of Tcf7/Tcf1 and Gata3 with age, suggesting their persistent stem-like state that impaired maturation. Aged Tusc2-KO NK cells also exhibited elevated expression of IL15Ralpha, FasL, and CX3CR1 at early stages, reflecting heightened activation potential and migratory responsiveness, yet failed to acquire effector markers such as CD16, indicating uncoupling between activation, licensing, and effector differentiation. Consistent with this impaired progression, the frequency of Stage IV (mature NK) populations markedly declined with age in KO mice, whereas WT mice maintained Stage IV NK-cell frequency. Conclusion: These findings indicate that TUSC2 is required for proper coordination of developmental transcriptional programs and for the acquisition of effector and metabolic competence during NK-cell aging, particularly within terminal effector subsets.