500 years, because that will give the Master Sword plenty of time to pass into legend as it was enclosed in the four walls of the Temple of Time, and for the possible war between the Sheikahs and the Royal Family, as mentioned by Impa in OoT, to die down.
The wars weren't between the Sheikah and the Royal Family. The Sheikah fought for the Royal Family.
I chose 500 yrs, because I am sticking to my guns about Koume and Kotake being in SS. And since in OoT Twinrova said they were 700 years old, this only makes sense to me.
I thought Kotake and Koume were about 400 years old in OoT. I think they say so before the die. One of the says that she is 400 and the other says that she is 380. So O guess they were about 400 years old in OoT.