Itachi joined Akatsuki when he was about 11-years-old. Almost two years before the Uchiha massacre.
Here's the timeline I've constructed based on the manga and the data book:
Note: AD = After the Fourth's Death
Kyuubi no Kitsune attacks Konoha. Naruto is born. Minato pwns Kitsune.
Itachi graduates as the best in the Academy at the age of 7
Itachi masters the sharingan at the age of 8
Itachi turns 10 and becomes a Chuunin.
Itachi meets Madara and becomes Madara's student.
Itachi's personality changes because of Madara's influence and teachings.
Itachi officially becomes an Anbu squad member.
Itachi becomes a double-agent for Uchiha and the Leaf.
Itachi turns 11 and becomes a member of Akatsuki.
Orochimaru tries to take Itachi as his host.
Orochimaru fails, has his hand cut off and quits Akatsuki.
Itachi turns 13 and becomes ANBU captain. (In retrospect, he didn't hold the position long...)
Later in that year - The Uchiha clan is slaughtered by Madara and Itachi.
Itachi leaves Konoha and became a missing nin.
23 July 8 AD
. Uchiha Sasuke turns 8.
Three years are up and Orochimaru takes takes an unknown woman as his second host.
Start of Naruto. 12 year old Naruto finally graduates.
1) Orochimaru attacks Konoha. Tries to make Sasuke his third host. Fails again and uses one of his prisoners.
2) Itachi and Kisame try to capture Naruto, but fail. Zetsu makes his appearance.
3) Jiraiya promises to teach Naruto, but leaves for three months first. When he returns, he and Naruto go off for training at 13.....
4) Akatsuki gathers and agrees to wait for three years... Chapter says, "their ambition... if they include the Kyuubi...everything will be in their hands..."
1) Naruto returns to Konoha at age 15 and a half....
2) Akatsuki gathers to rip Ichibi out of Gaara. Deidara and Tobi capture Sanbi. Hidan and Kakuzu capture Niibi Kisame captures Yonbi, bringing Akatsuki's total to seven tailed beasts...
3) Orochimaru prepares for Sasuke to become his fourth host, but is taken over by Sasuke.
4) The plot continues...
Alright, somethings you might say about my revelation:
This is some typo or mistranslation.
Who mistranslates numbers? lol.....
There are now two incidents of retrospect: One from Sasori and one from Kisame. When Sasori said Orochimaru left 7 years ago, Itachi was 18.
When Kisame says "It's been over ten years," in Chapter 353, Itachi is 21. There is no mistranslation. It is consistent.
Itachi was not 18 when he tried to kidnap Naruto. He had to have been older.
No, he was. He was 17 when the manga started, and 18 when the Part 1 ended. So says the Databook. If you believe that the Databook is incorrect about something as simple as characters ages, then the manga has plenty of evidence toward Itachi's age.
Sasuke was about to turn 8 ...... Itachi was 13 when Itachi murdered everyone.
This means that Sasuke was 13 and Itachi was 18 when he tried to kidnap Naruto.
Why would Itachi join Akatsuki at 11?! It makes no sense!
The motivations and secrets of characters are the plot twists that make stories enjoyable. Not understanding the reasoning right now does not mean that the information is false. Up until Chapter 242, we didn't know how Kakashi had a Sharingan, but that didn't mean he didn't have one.
Are you trying to say that Orochimaru was beaten by an 11-year-old chuunin?!
Yes. And it makes perfect sense. How long had Sasuke had Sharingan when Orochimaru tried to take his body? 3 years. How long had Itachi had Sharingan when Orochimaru tried to take his body? 3 years. Itachi and Sasuke had both had the same amount of experience with Sharingan and were at the same level of development. And Orochimaru received the same punishment for trying to take their bodies.
Well.... Orochimaru must have left Akatsuki years ago, before Itachi came, but snuck back when he heard Itachi joined to take his body.
Orochimaru says he left because of Itachi, time and time again... So do other characters. Please do not try to rearrange the sequence of events to make Itachi join Akatsuki at 13 or 14... The numbers don't lie.
Jiraiya even said that when Orochimaru joined, Itachi was a member...(Manga Proof: Chapter 143 pages 3-7) And we recently see Itachi recruiting Orochimaru's replacement, Deidara!
Well then, Itachi must have been spying on Akatsuki for Konoha and
--- Stop right there. Konoha did not know Akatsuki existed 10 years ago. Jiraiya knew, because he followed Orochimaru, but not Konoha. And Jiraiya did not tell Konoha until years later when he came back. (See above Manga Proof) Not very smart on the hermit's side, but that doesn't mean it isn't the truth. And once again, Jiraiya was the one who informed Konoha that Itachi was even a member of Akatsuki.
So then, Itachi was in Akatsuki and ANBU at the same time? And no one noticed?
Yes. According to Itachi's father and clansmen, when Itachi entered ANBU his personality completely changed. He started being difficult to talk to and aloof. This is months after he entered Akatsuki...
It is in this year that Itachi also goes on many "secret missions".... He never even bothers saying that they are ANBU.... Honest and candid until the end, Itachi..... Itachi flakes on responsibilities in his clan.... He then lectures Sasuke on the Purpose of the Shinobi.
Itachi says, "Shinobi usually live as hated people... To have strength means you become isolated and arrogant... Although at first, you only sought what you have dreamed for... "
Sounds pretty somber for a kid who was still a chuunin until that morning...
"Shinobi are tools, hated naturally for their very purpose: War." A speech that I don't mind saying was almost identical to Pain's speech to Hidan a decade later......( Chapter 329 pages 8-15 )
It is the same sort of speech he gave to Hidan.
Itachi became a chuunin at 10.
He was finally able to leave the village for missions. Somewhere, at some time, somehow he meets Madara.The Police Force was created by an ancestor of the Uchiha. Itachi and Sasuke discuss this when Itachi was atleast 10.5 years old and has been a chuunin for 6 months. Itachi then tries to flake on a mission with his father.
Itachi is officially hired by ANBU at 10.5 years, 6 months after becoming a chuunin.
But Itachi has changed since the time he was a chuunin. He is colder to his parents. He talks about secret missions
that he has to go on and he sees his line of work as something that is naturally feared and hated.
By 11, Itachi has become member of Akatsuki.
Orochimaru sees a promising youth in Itachi and tries to take his body using the Immortality Method he just perfected. It fails and Itachi chops off his hand.
Months pass. Itachi ranks high in ANBU. Itachi finds a secret room in his clan's temple, where a forbidden scroll is kept. It is about the true purpose of the Sharingan. With the information in these scrolls Itachi gains the unsightly power of MS.
Itachi expresses his feeling towards being a shinobi. "Am i unpleasant? Shinobi are hated people. To be strong is to be isolated."
He then proceeds to kill every member of his family except for his own younger brother, to whom he expresses respect for his brother's deep rooted hatred of him. "In order to reach the height of my capacity, I've lost all hope for this pathetic clan." Itachi mocks his clan for not reaching their capacity.
One month after his 13th birthday
, Itachi walks away from his home as a member of Akatsuki.
I don't believe you.
Well... That just isn't my problem. :)