Perhaps certain mental aspects can be learned at one age under certain circumstances, but at later ages or under inappropriate conditions learning is impossible, or greatly impaired. The lack of early education of the feral children could mean that they could never learn. It is difficult to draw conclusions from studies on feral children; each case was very different - the background of the feral child, the goals of the experimenter and the method of teaching all have to be taken into account. Of the five children, Kaspar Hauser appeared to be the most successful in learning how to talk, but Kaspar had not been raised in the wild.
I know, I know, I haven’t been posting. Apologies to my hypothetical reader.