Is there a name for the medical condition when a person is mature but behaves like a a little kid? (person can take care of his basic needs!)

Immaturity: The actual classification or name of the medical condition would really depend on: the actual age of the individual and their reason for acting less than their age. (by choice i.e. a psychiatric disorder or handicapped - congenital vs acquired etc). Did the individual mature normally as a child but then regressed? or did they stop at a certain level? Is there a history of trauma severe illness?