Abstract: An object of the present invention is to enable prevention of aging and extension of lifespan of a human or non-human organism by a method other than calorie restriction and administration of metformin. It is possible to prevent aging and extend the lifespan of a human or non-human organism by administering an agent comprising A) a xanthine oxidase/xanthine dehydrogenase inhibitor. In addition, it is possible to prevent aging and extend the lifespan of a human or non-human organism by combining A) a xanthine oxidase/xanthine dehydrogenase inhibitor and B) hypoxanthine, or a compound that is capable of being converted to hypoxanthine in body, by administering these simultaneously or administering these as a combination drug or a kit formulation.