Peter Panish
/ˌpiːtə ˈpanɪʃ/(also Peter Pannish)
adjective
Resembling or suggestive of Peter Pan, especially not fully grown up, childlike, immature.
Origin
Early 20th century; earliest use found in ‘Ian Hay’ (1876–1952), writer (real name John Hay Beith). From the name of Peter Pan + -ish.