"I was there, at the dawn of the Third Age of Mankind. It began in the Earth year 2257 with the founding of the last of the Babylon stations . . ."
The term was coined by John Sheridan following the Battle of Coriana VI and the end of the Shadow War. He characterised the first age as being the time when the races began in chaos and too primitive to make their own decisions then and the second when they were manipulated by forces that thought they knew what was best for them. The third age therefore being the time when the Younger Races could stand on their own, take responsibility for themselves and "make their own magic". The period is however recognised to have truly begun in 2257 with the founding of Babylon 5, though none knew it at the time.