Someone who is your peer is defined as someone “belonging to the same societal group especially based on age, grade, or status”. This Maxim instructs us to associate with our peers rather than those in other groups, not out of a sense of either superiority or shame, but because of similarities in understanding and experience. It is when we associate with our peers that we have the fewest gaps in communication (although those gaps do occasionally happen anyway) because we ‘speak the same language’ as the people around us.
What this Maxim is not telling us is to never associate with people from a different group if there is a good reason to associate with them. Sometimes you will find that they are your peers in an area that you had not considered. This Maxim is also not telling us to not associate with people who are better in an area than us if we are trying to improve in that area ourselves. It primarily speaks of social groups based on class in telling us to neither ‘go slumming’ or to ‘social-climb’ as we will not fit in in the other groups we would be associating with. Those are people who are unlikely to be your peers unless other factors intervene and as such, although we should try to understand their lives, we should be aware that we may not ever truly do so.