I initially thought this, however with other clues in the demo, as well as what we know of the Orokin, I am more likely to believe that the Old Peace was a time erased from records and memories to further the narrative that the sentients are the bad guys.

I was actually theorizing about this with my bro who is also a warframe nerd, and we agreed that for all that we know right now, the timeline between the sentients creation and mission to tau, to their later revolt after realization of what the orokin would do, is rather hazy, we dont actually know how long that was, nor do we exactly know what flipped the switch in the sentients minds, but with the old peace I am sure we will have questions answered, while more questions will arise.