The teenager “took a projectile to the head and died of his injuries in intensive care” on Saturday evening, a hospital source in the southern city told AFP on condition of anonymity.
“There were several seriously wounded people during the protests and one died. He was hit in the head by a bullet,” said Abdou Sane, coordinator of the opposition party Pastef in Ziguinchor.
Most Senegalese cities remained calm on Saturday but spontaneous demonstrations continued in Ziguinchor, a stronghold of jailed opposition figurehead Ousmane Sonko.
Sall said he postponed the election because of a dispute between parliament and the Constitutional Council over potential candidates barred from running.
He has said he wants to begin a process of “appeasement and reconciliation” and reiterated a commitment not to stand for a third term amid expressions of international concern.
Senegal’s parliament backed the move on Monday and voted to keep Sall in office until his successor takes over, which is unlikely to be before early 2025. His second term had been due to end on April 2.