Island backed account introduced by youngster (7)
I believe the answer is:
minorca
'island' is the definition.
(I've seen this before)
'backed account introduced by youngster' is the wordplay.
'backed' says the letters should be written in reverse.
'account' becomes 'ac'.
'introduced by' says to put letters next to each other.
'youngster' becomes 'minor' ('minor' can be a synonym of 'youngster'**).
'ac' written backwards gives 'ca'.
'ca' after 'minor' is 'MINORCA'.
(Other definitions for minorca that I've seen before include "holiday island" , "Land in Balearics" , "One of Balearic islands" , "Mediterranean island" , "Balearic island; O, cram in (anag.)" .)