Young person ordering green tea (8)
I believe the answer is:
teenager
'young person' is the definition.
(I know that young person can be written as teenager)
'ordering green tea' is the wordplay.
'ordering' indicates an anagram.
'green'+'tea'='greentea'
'greentea' is an anagram of 'TEENAGER'.
(Other definitions for teenager that I've seen before include "Young person" , "Old child or young adult?" , "troublesome youth" , "one that's not yet made a score?" , "youth, perhaps" .)