Dude I really don't think it was 10 years for shisui but we have to wait and see.
To see what? What I'm trying to achieve here is to either stop that the same people say that KA takes 10 years to cool down and then go out saying Shisui can't be toni because he is too young. They can't have it both ways. Doesn't add up.
Lets do some math now.
Shisui had to have used KA at least twice, once on Ao and once to know he had it.
He likely unlocked his MS at around, what, 12?
12 + 10 + 10 = 32
He was like the older brother of Itachi...? A 32 y/o isn't the older brother of a 13 y/o. Inconsistency? Nah, I just think Shisui didn't have the 10 year cooldown.
He couldn't be 16. No one unlocks MS at the age of 6 and I'm pretty sure KA must have been used more than once. Otherwise it wouldn't be famous.
Why couldn't he be 16 he could've awaken his Ms at 12 or 13 and he had KA in both eyes so he could've used them at different times.
He wanted peace, he was Itachi's mentor and he had the Mangekyou. I'm guessing his friend died in the 3rd war and he blamed himself or something (he probably also fought in it which is why Itachi was so affected by it or w/e). Getting the Mangekyou before 12 seems a little crazy, yeah, but you got Kakashi making chuunin at 6... I'm gonna say he was 22 at the time of the massacre.
Also, some of you are talking about KA having a faster cool down for him...who else used the technique beside him? Danzou did, yeah, and where did he get the information on the technique from? I'm gonna have to say Shisui himself, somehow (maybe Itachi told them after Shisui told him or something)... What I'm saying is, none of us have seen the technique really used with the waiting time included, and it was Shisui's, so I'm guessing the information given to us, was originally given by him.