And that is exactly why this term is appropriate in this context: people who categorize other people based solely on their age lack the mental capacity to realize the gross unsuitability of this classification. Also, their approach is usually deliberately hurtful. It is simultaneously stupid and evil. This is why the term „retard“ is appropriate here. It would not be appropriate to address an individual or a group with an actual mental disability.
Once you make it a circle, your storage space becomes infinite!