Ageing leads to the accumulation of differentiated, unconventional T cell populations. One such cell type is the virtual memory T (TVM) cell, which are semi-differentiated but antigen-naïve CD8 T cells. TVM cells have increased survival compared to conventional naïve CD8 T cells (TN) and accumulate in number with age, but become dysfunctional. Our work identified age-related shifts in T cell metabolism that did not correlate with function but may support the preferential survival of certain T cell subsets with age. With increased age, memory phenotype cells such as TVM cells exhibited increased mitochondrial load and spare respiratory capacity, despite a marked reduction in classic T cell functions (proliferation, IFNg production and cytotoxicity). In both mouse and human CD8 T cells, increased SRC was associated with heightened sensitivity to IL-15 and blocking IL-15 could reduce SRC in TVM cells. Our model suggests that IL-15 sensitivity and signalling increases in memory phenotype T cells in general and TVM cells in particular with age, to support increased SRC and cell survival. However, SRC is not a consistent positive predictor of conventional T cell function across the lifespan. In our ongoing work, we are using our model of T cell survival, function, metabolism and ageing to optimise the development of T cell-based therapies for older patients.