Does sin befall one who does not respect the elder and show mercy to the younger? And is this act forbidden, or is it merely a matter of Islamic manners? And what is meant by "our elder" in the Hadith: "He is not of us who does not respect our elder"?

The Hadith "He is not one of us who does not show mercy to our young ones and does not acknowledge the honor of our elders" indicates the prohibition of abandoning mercy towards the young and abandoning the acknowledgment of the honor of the elders. The term "elder" here refers to the old in age, and it also includes those of high status. Acknowledging honor has degrees; some are obligatory, such as not assaulting them, and some are recommended, such as waiving some rights. The common custom is referenced to determine who deserves to have their honor acknowledged.