Study of vrs health . Agree with wikipedia|: gerontology (from the greek ?????, geron, "old man" and -?????, -logy, "study of"; coined by ilya ilyich mechnikov in 1903) is the study of the social, psychological and biological aspects of aging. It is distinguished from geriatrics, which is the branch of medicine that studies the diseases of the elderly.
MD vs phd. Geriatrician is an actual doctor practicing medicine. Gerontologist somebody who just studies older people such as a phd.
Aging. Gerontologists are typically phd's who engage in research on aging; in some cases these are also mental health practitioners with a specialty in aging. A geriatrician is typically a medical doctor.