Old virtual queues technique for routing data packets in a packet switch

A packet switch includes virtual output queues for mapping data units of data packets from input ports to output ports of the packet switch. The packet switch selects virtual output queues based on old age indicators of the virtual output queues and routes data units mapped at heads of the selected virtual output queues to output ports of the packet switch. Further, the packet switch may identify a data unit of a multicast data packet mapped at the head of more than one virtual output queue and contemporaneously route the data unit to more than one output port. Additionally, the packet switch may update an old age indicator to indicate a virtual output queue is old if the virtual output queue maps an unserviceable data unit of a multicast data packet and the same data unit is mapped at the head of a selected virtual output queue.