Peter Pan syndrome: Term coined by pop psychology author Dan Kiley in his book "Peter Pan syndrome: Men Who Have Never Grown Up."
Peter Pan is in reference to J. M. Barrie's classic 1904 play in which a boy who refuses to grow up teaches Wendy and her younger brothers how to fly and then it's off to magical Neverneverland for adventures with mermaids, Indians, and wicked Captain Hook and his pirate crew. The play's full title was "Peter Pan, or, The Boy Who Would Not Grow Up."
The Peter Pan syndrome is not at this time a medically accepted syndrome.
Mr. Kiley also coined another J.M. Barrie-inspired term in his book "The Wendy Dilemma : When Women Stop Mothering Their Men."