Definition of young adjective from the Oxford Advanced Learner's Dictionary

Oxford3000

young

adjective
jʌŋ
 
; jʌŋ
 
 
younger
ˈjʌŋɡə(r)
 
; ˈjʌŋɡər
 
youngest
ˈjʌŋɡɪst
 
; ˈjʌŋɡɪst
 
1 having lived or existed for only a short time; not fully developedyoung babiesa young countryCaterpillars eat the young leaves of this plant.a young wineThe night is still young(= it has only just started).
Opposite
old
2 not yet old; not as old as othersyoung peopletalented young football playersI am the youngest of four sisters.In his younger days he played rugby for Wales.I met the young Michelle Obama at Princeton.Her grandchildren keep her young.My son's thirteen but he's young for his age(= not as developed as other boys of the same age).They married young(= at an early age).My mother died young.
Opposite
old
3 consisting of young people or young children; with a low average ageThey have a young family.a young audience4 suitable or appropriate for young people
Synonym
youthful
young fashionThe clothes she wears are much too young for her.
5 young man/lady/woman used to show that you are angry or annoyed with a particular young personI think you owe me an apology, young lady!6 the younger used before or after a person's name to distinguish them from an older relativethe younger Kennedy (British English, formal) William Pitt the younger compare the elder at elder adjective, junior adjective (3)
Idioms

be getting younger

(informal) used to say that people seem to be doing something at a younger age than they used to, or that they seem younger because you are now olderThe band's fans are getting younger.Why do police officers seem to be getting younger?

not be getting any younger

(informal) used when you are commenting that time is passing and that you are growing olderWe need to start thinking about our retirement. We're not getting any younger, you know.

young at heart

thinking and behaving like a young person even when you are old
My father is 76 but he's still young at heart.
more at (have) an old head on young shoulders at old, you're only young once at only adverb