IPA: /ˈjuːθfəl.nəs/
KK: /ˈjuːθfəl.nəs/
The quality or state of being young, often associated with energy, freshness, and vitality.
Her youthfulness was evident in her energetic personality and bright smile.
Youthfulness → It is formed from "youth" (from Old English *geogð*, meaning the period of being young) and "-fulness" (meaning the state of being full of). The word "youthfulness" means the state of being full of youth or characteristics associated with being young.
Think of the state of being 'full of youth' — 'youth' refers to being young, and '-fulness' indicates a state or quality.