youth·ful [youthfulyouthfullyyouthfulness] BrE [ˈjuːθfl] NAmE [ˈjuːθfl] adjective 1. typical of young people •youthful enthusiasm/energy/inexperience 2. young or seeming younger than you are •She's a very youthful 65. Derived Words: ↑youthfully▪ ↑youthfulness