Green tea brewed for youngster (8)
I believe the answer is:
teenager
'youngster' is the definition.
(thesaurus)
'green tea brewed' is the wordplay.
'brewed' indicates an anagram.
'green'+'tea'='greentea'
'greentea' anagrammed gives 'TEENAGER'.
'for' acts as a link.
(Other definitions for teenager that I've seen before include "Youngster" , "one that's not yet made a score?" , "one with an unpredictable nature" , "Generate (anag)" , "one no longer twelve?" .)