Domestic violence, verbal violence by parents, divorce, severe punishment, parents' use of alcohol or drugs, experience of depression by one of the parents, experience of suicide in parents, imprisonment of close relatives, sexual and physical violence.
This and similar adverse experiences lead to the formation of emotional disturbances and often force people even in adulthood to protect themselves from the possible repetition of unpleasant episodes.
For obvious reasons, PTSD can form at a later age, if a person has been abused, had an accident, became a participant in hostilities.