While the concept of the adult child was originally developed to explain the difficulties of men or women who grew up with an alcoholic or addict in the home, it is.
As an adult, do you believe you are treated like a child when you interact with your parents? Are you continuing to live out a childhood role with the parents?.
What is an adult-child? Well, it's when you're basically a child living in an adult body. Sure, you enjoy wine and the occasional R-rated movie, but you also love.
Most women/men find this highly unattractive and hence the adult child generally stays single either forever or until they finally do something about their situation.