The 'original' Warriors of Light were actually the original players of FFXIV 1.0 that was shut down (which ARR replaced). 1.0 players that passed a certain point in 1.0's storyline (the Lunar Transmitter fight) started ARR with a different opening where they teleported into the game like the 'New Beginning' opening movie and walked to their starting city, and have some slighty different dialogue throughout ARR's story, and eventually
at the end everyone remembers that they were at Cartenau and thus was one of the 'original' Warriors of Light now returned and are celebrated as such accordingly.
From the point of view of the 'default' story though (that new players get, along with returning 1.0 players like me who never statisfied that 1.0 story requirement), the original Warriors of Light never returned as far as Eorzea knew, but instead became an ideal to live up to for new adventurers who 'answered the Crystal's Call' and flocked to Eorzea to defend it. Also, and this is a spoiler for you,
at the end due to being 'chosen' by Hydaelyn with both the Echo and the Blessing of Light and your actions in gathering the six Crystals of Light, slaying the Primals, destroying the Ultima Weapon, uniting Eorzea together and driving away Lahabrea, you become a new Warrior of Light yourself, thus making whether you were one due to your actions during the Calamity or have just become one now moot, the point is, in the story from your point of view your character is the Warrior of Light.
Hopefully that hasn't been too confusing for you.