Schematic overview of strong interconnection between aging and cancer. The discussed biomarkers of aging are summarized as well as the clinical symptoms of frailty. The aging process and cancer share several biological processes impacting oncological decision making. However, treatment choices, toxicity and tolerability and treatment efficacy are highly influenced by age and more importantly frailty status. Taking all this together, age and frailty have an immense impact on the risk of developing cancer, cancer biology, prognosis, and therapy choices and thus the outcome for older patients with cancer.