also: ピーター・パン・シンドローム
noun
Peter Pan syndrome
A pop-psychology term describing an adult who avoids adult responsibilities and maturity. Used in Japanese as a loanword concept.
彼はいつまでも子供っぽくて、まるでピーターパンシンドロームみたいだ。
He's so childish no matter how old he gets; it's like he has Peter Pan syndrome.