80's baby means you were born in the 80s or a baby in the 80s. 80's KID meant you were a kid/teen in the 80s.
Why is that so difficult for you people to understand? Basically you are saying "You aren't an 80's baby because you were a baby in the 80's."
Do you know what a baby is, period?
First time I ever heard the term; Jay-Z, Go Crazy - "See I'mma ‘80s baby, mastered Reaganomics"
And he was born in '69 (he was a teenager in the 80's)
That's where, it seems, ppl started usin' it