Read this only after you've read the book and you can't figure out the timeline. Otherwise heavy spoilers ahead.
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A lot of you guys have trouble keeping up with the timeline so here's an explanation.
First, the beginning. It takes place 6 months before the Naruto's birth. That's when Kenshin was born. That is, April 9th. Akane was born 2 years before him, on February 14th.
Next, the Uchiha massacre. It happened when Kenshin was 7 and a half years old, while Akane was 9.
After that, there's Kana's disease. It happened a few months after the Uchiha massacre, when Kenshin was about 8.
She got bedridden after 3 years of her disease, but because of Kenshin's care and devotion, she survived for another 4 years like that.
So that makes him about 15 by the time Kana had to be brought to the hidden leaf, which puts it 6 months before the beginning of Naruto Shippuden. That is why Tsunade is in the hidden leaf as she is hokage.
Akane became a genin at 13, alongside her teammate Maki who is slightly younger than her.
Also, Kakashi should know how his mangekyo sharingan works. He's a smart guy, he wouldn't want to have an uncertainty on his hands.
He probably figured out how his mangekyo sharingan worked after a couple of uses. And he stated that he did so sometime before the start of Shippuden, but the exact time wasn't stated.
He probably began working on it after his encounter with Itachi made him realize that there was another stage to the sharingan, and after some tinkering, he probably activated his mangekyo.
So him knowing how it works six months prior to the beginning of Shippuden doesn't contradict anything.
So I hope that helps clear everything up. I'll update this in the future as I deem necessary.