Just to confirm, this is wrong. I know of a caique who was separated from his clutchmates and went to a new home and plucked his chest bare. He was 4-5 months old. The new owner had also purchased a friend for him but she was a little younger and still with the breeder. Once she did get the other bird home and in the flock the original caique stopped plucking and grew all his feathers back. This was all in a bird who was less than a year old. So perhaps, it is unusual but definitely possible.I thought I read somewhere that parrots who are not even one year old don't pick/pluck unless there's a medical issue. I could totally be wrong though. I would definitely get a check up though to be sure.
Of course you do want to rule out a medical issue first.