Great Elder Toad Sage is the Summon of Sage of Six Paths.

[Lentz]

also the age of "Great toad Sage" is More than 1000 Years So he was alive when Sage Fought Juubi.
plus his Size is atleast 5x Gamabunta. gamabuntas size is Nearly the same as full power kyubi.
So By that you can see how Sage fought Juubi. the size diifrence was Covered when SO6P Summoned "Great toad Sage" cause its possible that Juubi size is same as Great toad Sage.

Anyways I am Sure SO6P is related with Great toad sage

Suuuure.

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[Maunten]

How is a human related to a toad?

Saw an opening and took the shot huh...

 

[Bogard]

He is not the only one who can predict in the futur since we've already seen thanks to Kabuto that the great Snake could do the same also. So if your theorie is true then maybe the Great Toad, the great Snake and another one were all summoning from SO6P