Board Thread:Character Discussion/@comment-4851603-20160430054720/@comment-25926288-20160430125635

Yes, Hades being the oldest and denied his birthright makes for a better parallel to Zelena and Regina (that they were doing) and for the plot.

Chances are Zeus is still younger than Hades, just they took a phrase and twisted it. I'd like to imagine after Kronos swallowed his kids, they just calimed Zeus was the oldest while the other kids were going to be "reborn" or spit out after Zeus.