Green’s Dictionary of Slang

a young person.

1978		(con. 1965) J. Carroll The Basketball Diaries 98: [T]wo blueboys showed up [...] [T]hey looked over the chicks and asked ages and proof, kicked a few youngies out [...] and then tipped off.
1999		Guardian 12 July 16: His punk era hits inspired a golden glow in the oldies and indulgent foot-tapping in the youngies.