How long was Kakashi Hokage in Naruto

At what age did Kakashi Hatake become a jounin?

Kakashi became a Genin at the age of 5 and Chunin at the age of 6.

Obito became a genin at the age of 9 and a chunin at the age of 11.

Around the time Obito became Chunin, Kakashi was promoted to Jonin.

Obito then "died" at the age of 13 years , almost two years after being promoted to Chunin.

From this thread about Narutoforums (focus on mine):

It is impossible for both Kakashi and Obito to be able to play during Kakashi Gaiden 13 Years old as it confirmed one age difference of at least 4 years between Kakashi and Obito when it was confirmed that they are both Genin teammates during the Chuunin exams. They entered the academy at the same time and everyone graduated from the academy as teammates. Kakashi was at least 4 years younger than his two teammates at all times. It's impossible that Kakashi was a 13-year-old Jonin during the Kakashi Gaiden.

This idea that he was 13 isn't even supported in the data books either. It is time we all got our facts straight. If Obito died at age 13, then Kakashi was most likely during the Kakashi Gaiden 9 years old. It is impossible that these two teammates were ever the same age.

Kakashi was 13 during the Kyuubi attack on Konoha . There is a 4 year difference between the events of the Kakashi Gaiden and the events of the night Naruto was born.

Also from Obito Uchiha's discussion page on the Naruto Wiki

Obito-Kakashi's timeline is primarily based on the anime and manga / databook material prior to Chapter 599. Kakashi graduated from the Academy when he was 5 years old, Rin and Obito when 9. Obito is 3 years 7 months older than Kakashi. They all took the same Chunin exam, with Kakashi managing to become Chunin at age 6 while Obito failing at age 10. Obito trained hard, passed the next exams and became a chunin at the age of 11. Obito was crushed by boulders at the age of 13, which means that Kakashi was 9-10 years old by the Gaiden at the latest. Kakashi is now 31, so Obito died when he was 34.

As for the youngest Jonin part, nobody really knows how many official Jonin there are. If I remember correctly, Itachi was not officially declared a Jonin. He entered the Anbu after becoming a Chunin. Kakashi could so be the youngest Jonin. There is no definitive answer.

Edit (Courtesy @Merrice Henderson):

There is evidence that Kakashi made Jonin the same year Obito and Rin made Chunin. This is an effort from Obito's Wikia page:

Obito was eager for Rin's attention and trained tirelessly. Eventually he rose to the rank of chunin himself. His excitement was short-lived when Kakashi soon became a jonin and again earned Rin's praise and Obito's resentment. "

So Obito 11 was confirmed when he became a chunin. If we go on the theory that Kakashi is 4 years younger (which I tend to think) then he was 7 when he made Jonin. That would effectively make him the youngest Jonin ever. If Kakashi was the same age as Obito and Rin, then there are a few years to consider, such as:

  • "Who was he with after graduation, when Obito and Rin were still in the academy?"

  • "What happened to Kakashi's other teammates or did he take a break for that time?"