uncountable the time in someone’s life when they are youngIn his youth, he had travelled and seen much of the world.
the energy/enthusiasm/innocence of youth
relive/recapture your youth: The visit was more than just a chance to relive her youth.
misspent youth (=time spent doing silly or bad things when you are young): Adults who choose to go to college in later life are perhaps making up for a misspent youth.