Portmanteau for a grown-up who hasn't yet grown up

• Lord half-cut in tartan? Maybe he can't grow up
• Grown-up who's not quite grown up

Wikipedia Word definitions in Wikipedia
The portmanteau coinages kidult , rejuvenile , adultescent refer to adults with interests traditionally seen as suitable for children . It can also have other meanings, such as a parent who enjoys being a parent due to spending quality time with their children, ...

Wiktionary Word definitions in Wiktionary
n. (context informal marketing sociology English) An adult who participates in youth culture and activity traditionally intended for children.