Green’s Dictionary of Slang

(Aus./US) a juvenile delinquent.

1959		A Sexton Letters 59: I failed most things (a real juvenile delink) [HDAS].
1963		J. Blake letter 2 Aug. in Joint (1972) 214: Kaplan sends the blond juvenile delink out with ten dollars to get some ‘Grass’.
1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxiv 4/3: delinko: A young criminal. Delinquint is the popular name nowadays used by the nice people to describe young hoodlums.
1983		R. Aven-Bray Ridgey-Didge Oz Jack Lang 24: Delinko Juvenile delinquent.