There are two major theories about the origin of this word, both of which probably have elements of truth to them.
a) Twink comes from an acronym T.W.I.N.K. "Teenage, White, Into No Kink."
b) Twink is a shortening of the name for the famous "TWINKIE" snack cake: a tasty, cream-filled snack with no nutritional value. The phallic shape of the "TWINKIE" snack cake should not escape the reader's attention.
Often also being naïve, and cute, with nothing upstairs.
The gay equivalent of the mainstream `chick'.