Youngster of little importance? (5)
I believe the answer is:
minor
I believe this clue is a double definition.
'youngster' is the first definition.
('minor' can be a synonym of 'youngster')
'of little importance?' is the second definition.
(I've seen this before)
(Other definitions for minor that I've seen before include "Young person below voting age" , "Of small importance" , "Of less importance" , "Deceptively realistic (art)" , "Not major" .)