From a purely chronological point of view, the psychiatric disorders of the aged fall into three main groups: the presenile disorders, which begin as early as the fourth decade; disorders of the involutional period, which occur between 45 and 60; and the senile mental diseases, which have their onset after 60 or 65. But in mental as well as physical health the transition from physiological to pathological aging is influenced by many other factors besides the years the patient has lived. Individual variation in personality is as great in the older as in the younger age groups, and physiological and psychological age by no means always parallel chronological age.
Although certain psychological problems are common to all who reach the period of senescence, it is indeed fortunate that the overwhelming majority of the aged retain their mental faculties to the full. In a study of 477 individuals over 65 who
Himler LE. PSYCHIATRIC ASPECTS OF AGING. JAMA. 1951;147(14):1330-1331. doi:10.1001/jama.1951.03670310020007