Yes, this may be considered "liveposting" since the stream is still on-going, but it is of more interest to the general discussion revolving around a theory that pops up from time-to-time. So, from the Airi stream, some possibly interesting info regarding the theory of who the ultimate hag in PC is:
Airi was talking about how some of the Gen 1 members, particularly Lia and Uruka, find it weird to be called "senpai" by Airi, especially after meeting in real life. Apparently, Iori also finds it awkward, who told her "Airi, you don't have to call me senpai". This would seem to dispel the theory that Iori may be the oldest member like many have theorized, but she says something a little later that may indicate Iori still being the one. She went on to claim that if they were more used to the JP culture, they may not mind it, like Tenma. She then said, and I quote:
"But definitely Uruka and Lia would probably be a bit more like "Please don't call me Senpai". Iori being an exception."
So it kind of circles around without any definitive answer, but we may be able to interpret this as Iori being older, but still preferring not to being called "Senpai" since Airi claims Iori, Lia, and Uruka prefer not to be called senpai, but Uruka and Lia being a different case than Iori. And since we know Lia and Uruka are younger than Airi, that exception could very well be that Iori is actually older than Airi.
But hey, it's just a theory. An autistic theory. Thanks for reading.