Comments of chapter undefined of Eroninja

The bit about Zetsus actions of eating and raping with all the blood relations to the sage is actually a really plausible idea for Zetsu to come up with initially in such chaotic times. I'm a bit lost on the talks of the Uchiha and such clans being over 10,000 years old though. When the biju are in canon 1k and those slightly less. I can get that it doesnt have to be the same but 10,000 year old clans?

Thanks