Metformin, an FDA approved first-line drug for the treatment of type 2 diabetes, has known beneficial effects on glucose metabolism. Evidence from animal models and in vitro studies suggest that in addition to its effects on glucose metabolism, metformin may influence metabolic and cellular processes associated with the development of age-related conditions, such as inflammation, oxidative damage, diminished autophagy, cell senescence and apoptosis. As such, metformin is of particular interest in clinical translational research in aging since it may influence fundamental aging factors that underlie multiple age-related conditions. The investigators therefore propose a pilot study to examine the effect of metformin treatment on the biology of aging in humans. Namely, whether treatment with metformin will restore the gene expression profile of older adults with impaired glucose tolerance (IGT) to that of young healthy subjects.