Peter Pan Syndrome Meaning

(idiomatic) The supposed psychological phenomenon of immaturity among some men and women, who, like the fictional character, remain childish and fail to assume appropriate adult social roles and responsibilities.

Example: 1989, Alice Hall Petry, "Alice Walker: The Achievement of the Short Fiction," Modern Language Studies, vol. 19, no. 1 , p. 17:
  The husband himself (called "he" to emphasize his role as Typical Male) comes across as a rather dense, naughty adolescent boy. He is clearly suffering from a terminal case of the Peter Pan syndrome.