rejuvenile
A member of the 'Boomerang Generation', or any person older than adolescence who, instead of marrying and/or raising a family, continues the pastimes and spending habits of adolescence. Mentioned in the May 15th issue of the New York Times, Movie section.
"So he's 30, lives in his mom's basement, and has a huge comic collection"
"Yep, he's a rejuvenile"
"Yep, he's a rejuvenile"