Don't forget . . . Obi-Wan was allowed to make Anakin his apprentice right after he became a Knight. And honestly . . . he was no more ready for that role than Anakin was.
I know the novel said he was in his mid twenties, but he seemed so much younger in TPM -- like around twenty.
If Obi-Wan was 25 when he took his first apprentice- and Anakin was 20- that's a 5 year difference. Not huge. Are there EU Jedi who became Knights, and took apprentices almost immediately afterward, when they were in that age range?
Ewan McGregor and I are the same age; therefore I know he was 25 when he filmed TPM. As far as whether either he or Anakin were too young to take an apprentice, I think the Jedi would take maturity and skill level--and in Ahsoka's case, the mutual need to train and be trained--into account before chronological age. The Clone Wars movie and novelization indicates that the Council gave Ahsoka to Anakin as much for Anakin's development as for hers.
Anakin was 9 years old when he became Obi-Wan's apprentice. Obi-Wan did not even have time enough to develop on his own as a Jedi Knight, when he became Anakin's master. If that was the Jedi's idea of training, I believe it was not a good one.
I was thinking of whether Obi-Wan was "more prepared" when he took on Anakin, than Anakin was when he took on Ahsoka". Thus why the "5 year difference" - between "Mentor Obi-Wan" and "Mentor Anakin".
Because Anakin is incapable of training himself, much less train a Jedi. He refuses to learn self-control nor self-discipline and I find it laughable that the Jedi council believes that Anakin can teach a jedi padawan those same attributes when they won't even grant him the rank of "master". They shouldn't even grant him the rank of Jedi knight and his actions with the Tuskens, Dooku, and post-Mace Windu's death shows us why.
I don't think that the Jedi's rationale for giving Ahsoka to Anakin to train was a good one either. I do think that a person can learn by being put in a position to lead or teach because in such a situation, he or she has to learn and take responsibility for the material. However, Yoda's comment that giving Ahsoka to Anakin would teach him to "let go"...how exactly was that supposed to happen? Yoda ignored a basic part of Anakin's personality. Anakin does do anything halfway in his personal relationships--he cares passionately and therefore "letting go" and being "detached" is not something the Jedi can just tell him to do or teach him to do. I think there was plenty that Ahsoka could learn from Anakin, but giving a 20-year-old new Knight an apprentice (which from my understanding was not common practice, since apparently Obi-Wan getting an apprentice as a new Knight was unusual) in order to teach him to "let go" was not the best idea.
Not one of them was capable of training him or herself. And honestly? I believe the Jedi Council was just as wrong to allow Obi-Wan to train Anakin, so soon after becoming a Knight. He proved that he was not really prepared for the task, as he eventually confessed to Luke. I believe that hardly any of them were good at letting go. Anakin certainly proved this. Padme proved this by insisting that her marriage to Anakin remain a secret. She seemed more terrified of the Jedi Order's influence on Anakin than the possibility of him getting killed during the war. And the actions and decisions of Obi-Wan, Mace and Yoda in AOTC and ROTS seemed to indicate that they were willing to do anything to maintain their position within the Republic and their existence.
It is possible that the Jedi Council felt some negative emotions slowly taking over Anakin. So they decided that perhaps having a young apprentice, just as eager as he once was, would change his overall attitude. And as far as I remember from TCW (I haven't watched too much of it), their relationship started a bit rough, but then it became friendship.