Youngster seen by an islander (5)
I believe the answer is:
cuban
'islander' is the definition.
(I've seen this before)
'youngster seen by an' is the wordplay.
'youngster' becomes 'cub' (I've seen this before).
'seen by' says to put letters next to each other.
'cub'+'an'='CUBAN'
(Other definitions for cuban that I've seen before include "Republican" , "One from Havana" , "from island republic" , "Relating to Castro's isle" , "Nationality of citizen of Havana" .)