Lymphomas represent a growing health concern in aging populations, with diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), and Hodgkin lymphoma (HL) being the most prevalent subtypes in elderly patients. The incidence of DLBCL rises sharply with age, and FL commonly presents in individuals over 60, while HL shows a second peak in later decades. Epidemiologic data highlight significant geographic variation, with higher incidence in Europe and North America compared to Asia, yet demographic shifts are driving rising case numbers across all regions. Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) has become the cornerstone of diagnostic and therapeutic management in this population. PET/CT enhances staging accuracy, reduces the need for invasive procedures such as bone marrow biopsy, and provides prognostic biomarkers including metabolic tumor volume and total lesion glycolysis. Interim and end-of-treatment PET assessments are powerful predictors of treatment response and survival, guiding risk-adapted therapy even in elderly patients with comorbidities. However, interpretation requires careful consideration of age-related factors such as inflammatory uptake, growth factor use, and metabolic comorbidities. Overall, FDG-PET/CT is indispensable in elderly lymphoma patients, enabling precise staging, individualized treatment planning, and improved outcome prediction while balancing diagnostic accuracy with clinical context.