And we also know that Zoan Devil Fruits have “minds” of their own. So, that means, Zoan Devil Fruits are actually not just longlasting items, but these are also immortal living creatures.

Now my theory is:

“The Gorosei are individuals whose souls have been fed to Mythical Zoan Devil Fruits in the past by a user of Ope Ope no Mi”.

So, basically, what was being done to them was the opposite of eating Devil Fruit, the Mythical Zoan Devil Fruits ATE the Gorosei, and this feat could only be achieved by a user of Ope Ope no Mi, just before he/she performed Immortality Surgery on Imu.

Or maybe another way of understanding this is: the Souls of the Gorosei, and the Wills of the Mythical Zoan Fruits, were switched by that past user of Ope Ope no Mi.

This is why the Five Elders have the “characteristics” of Devil Fruits:

-No longer go through aging and are immortal (just like the Devil Fruits won’t become rotten nor decay)

-Could teleport and regenerate (just like Devil Fruits which will respawn somewhere else if the users die)

That’s it my theory about the origins of the Gorosei’s ridiculous abilities.