Once rebuked poet about Liberal's early years (9)
I believe the answer is:
childhood
'early years' is the definition.
(I've seen this before)
'once rebuked poet about liberal's' is the wordplay.
'once rebuked' becomes 'chid' (archaic past tense of 'chide').
'poet' becomes 'hood' (I've seen this in other clues).
'about' is an insertion indicator.
'liberal' becomes 'l' (abbreviation).
'chid'+'hood'='chidhood'
'chidhood' enclosing 'l' is 'CHILDHOOD'.
(Other definitions for childhood that I've seen before include "Early years" , "Extreme youth" , "Between infancy and adolescence" , "Time of immaturity" , "Immature state" .)