After knowing the power of the Ope Ope No Mi, I am almost sure that someone has already used that power. Otherwise it is not possible for anyone to know what it will do. Also, it is quite possible since the fruit is reborn after the original owner dies.
Now, given the set of characters in OP, my first guess would have been Celestial Dragons but we know they can die. We know that the Yonkos do not have this power or they would simply conquer the world. The most probable answer is Gorosie. Those oldies have already used this DF on them and hence, they are the rulers of the world and they possess vast knowledge. It is not known if this ability grants youth or a person just cannot die from anything, otherwise killing gorosie would be impossible. Thoughts?
Now, given the set of characters in OP, my first guess would have been Celestial Dragons but we know they can die. We know that the Yonkos do not have this power or they would simply conquer the world. The most probable answer is Gorosie. Those oldies have already used this DF on them and hence, they are the rulers of the world and they possess vast knowledge. It is not known if this ability grants youth or a person just cannot die from anything, otherwise killing gorosie would be impossible. Thoughts?