Youth stirring green tea (8)
I believe the answer is:
teenager
'youth' is the definition.
(I've seen this before)
'stirring green tea' is the wordplay.
'stirring' indicates anagramming the letters.
'green'+'tea'='greentea'
'greentea' is an anagram of 'TEENAGER'.
(Other definitions for teenager that I've seen before include "one with an unpredictable nature" , "Adolescent" , "one that's not yet made a score?" , "14, perhaps" , "Youngster" .)