Which are the psychological disorders least common among elderly?

The field of psychology which deals with the mental health of older people is known as Geropsychology. It applies the methods and knowledge of psychology to understand and help elderly persons and their families maintaining well-being, overcoming obstacles, and achieve maximum potential during later life.

The psychological disorders least common in the elderly are:

Personality disorders: Personality disorders refer to a pattern of thinking, behaving, and feeling that deviates from normal, causes problems or distress, and lasts for a long time. Personality disorders generally begin in the teen years as personality develops and grows. As the age increases, the prevalence of personality disorders decreases. Hence, personality disorders are not commonly found in the elderly. 

Eating Disorders: Eating disorders are severe psychological disorders characterized by eating, body weight, or shape and exercise that become an unhealthy preoccupation in an individual's life. Eating disorders usually develop in the teen years or the 20s. The onset of eating disorders in the elderly is not common. 

Post-traumatic Stress Disorder: Refers to failure to recover after experiencing a traumatic event. PTSD is common in age between 18- 24 years and is hardly found in order people. 

Obsessive-Compulsive Disorder: It is characterized by unreasonable thoughts and obsessions that lead to compulsive behavior. The mean age of OCD onset is between 20- 25 years, and the onset of OCD in people older than 50 years is relatively unusual.