(adj) Describing an object, person, or situation that is ill-formed, damaged, or just plain messed up.
Likely from "premature" + "mutated".
First known occurrence in common parlance: January 1987, Atlanta, GA.
"Don't be smokin' crack and drinkin' 'cause you'll have them prematated babies."
"I can't believe she's wearing the dress that her mother made to prom--it's totally prematated."
"She was really kind of pretty until she got that botched facelift, and now she looks all prematated."