Popular novice upstanding in my youth (8)
I believe the answer is:
minority
'youth' is the definition.
(thesaurus)
'popular novice upstanding in my' is the wordplay.
'popular' becomes 'in'.
'novice' becomes 'tiro' ('tiro' can be a synonym of 'novice'**).
'upstanding' is a reversal indicator.
'in' is an insertion indicator.
'tiro' written backwards gives 'orit'.
'in'+'orit'='inorit'
'inorit' going into 'my' is 'MINORITY'.
(Other definitions for minority that I've seen before include "Lesser number" , "Relatively small group of people" , "Smaller number" , "Less than half" , "Smaller part" .)