There Once Was a Group of Teenagers - the Bronze Saints

There was once a group of teenagers who lost their parents and became orphans when they were still in their infancy. When they were children, they were supposed to have a happy childhood, but were sent to various parts of the world to receive rigorous training. When they grew up, while their peers were enjoying their youth, they were fighting fiercely for the peace of the earth. Finally, the war is over, but they can never return to their peers because their hearts have grown old. Conception: