noun. An adult who has maintained or adopted a lifestyle associated with young people, especially in matters of fashion, entertainment, and recreation.

noun. (marketing, sociology) An adult who participates in youth culture and activities traditionally intended for children.

"Gagliardi is a self-described funny man, historian, teacher and "kidult" - another one of his words-in-waiting with the following definition: someone, who like him, "has never made it adult.""

kidulthood  

kilt