State furiously: 'I'm an adult!' (5,4)
I believe the answer is:
tamil nadu
'state' is the definition.
(Indian state)
'furiously i'm an adult' is the wordplay.
'furiously' indicates an anagram (the letters move around energetically or furiously).
'im'+'an'+'adult'='imanadult'
'imanadult' anagrammed gives 'TAMIL NADU'.
(Other definitions for tamil nadu that I've seen before include "Southern state of India" , "Southern Indian state" , "state bordering Kerala" .)