Ageing
Ageing or aging (see spelling differences) is the process of becoming older. The term refers especially to human beings, many animals, and fungi, whereas for example bacteria, perennial plants and some simple animals are potentially immortal. In the broader sense, ageing can refer to single cells within an organism which have ceased dividing (cellular senescence) or to the population of a species (population ageing).
Gerontology
Gerontology is the study of the social, cultural, psychological, cognitive, and biological aspects of ageing. The word was coined by Ilya Ilyich Mechnikov in 1903, from the Greek γέρων, geron, "old man" and -λογία, -logia, "study of". The field is distinguished from geriatrics, which is the branch of medicine that specializes in the treatment of existing disease in older adults. Gerontologists include researchers and practitioners in the fields of biology, nursing, medicine, criminology, dentistry, social work, physical and occupational therapy, psychology, psychiatry, sociology, economics, political science, architecture, geography, pharmacy, public health, housing, and anthropology.