Green’s Dictionary of Slang

1. an attractive young man.

1967–8		Baker et al. CUSS 225: Yummy A sexually attractive person, male.
1972		B. Rodgers Queens’ Vernacular 218: little yummies teenagers.

2. an attractive teenage girl.

1970		R. Crumb [cartoon caption] Honeybunch Kaminski, 13, of L.A. What a little yummy!
1979		D. Gram Foxes (1980) 77: A well-proportioned blond chick, a baby-faced yummy.