But he who hates his brother is in the darkness, and walks in the darkness, and doesn't know where he is going, because the darkness has blinded his eyes.

 We do not say that there is no thought of age groups in this. There almost certainly is; but John has a way of saying things which can be taken in two ways, a narrower and a wider; and, while the narrower meaning is here, we must go beyond it to find the full meaning. 