bright young thing

noun2

1. •
   One who is youthful, clever, eager, and high-spirited in manner and attractive in appearance.

   • YOUNG COLLEGE MAN, travelled, slightly peeved and irked, not disenchanted, would relish hearing from bright young things with gay outlook, brilliant notions. — 1952
2. •
   (historical) Any of a group of bohemian young aristocrats and socialites in 1920s London.