Approximately 35% of US adults over 65 are obese, highlighting the need for therapies targeting age-related metabolic issues. Fibroblast growth factor 21 (FGF21), a hormone mainly produced by the liver, improves metabolism and extends lifespan. To explore its effects without developmental confounders, we generated mice with adipocyte-specific FGF21 overexpression beginning in adulthood. When fed a high-fat diet, these mice lived up to 3.3 years, resisted weight gain, improved insulin sensitivity, and showed reduced liver steatosis. Aged transgenic mice also displayed lower levels of inflammatory immune cells and lipotoxic ceramides in visceral adipose tissue, benefits that occurred even in the absence of adiponectin, a hormone known to regulate ceramide breakdown. These results suggest that fat tissue is a central site for FGF21's beneficial effects and point to its potential for treating metabolic syndrome and age-related diseases by promoting a healthier metabolic profile under dietary stress and extending healthspan and lifespan.