The link I gave in the answer? I am not so sure about it, I actually tried to reach them separately and in English forms because I don't know Arabic or Urdu. But I couldn't reach. They are mostly looks like printed books.
But, I listened lots of Profs. According to them, and they were using the same hadiths, the link I gave looks appropriate. I am a Turk and in Turkey there is a department called Presidency of Religious Affairs. These profs are graduated from faculties of theology, then academically continued to become profs and they are mostly belong to the Presidency of Religious Affairs. It seems to the conclusion I gave to you is the common conclusion of this department.
If I remember right, this claim (year between 17-20) is first announced by some Arab or Persian scholar in 1930s. Then a scholar from Turkey read it, and made research about it in 1970s or 80s.
He is greeted with huge resistance in Turkey back then. In order to prove he is wrong or to support him, lots of dr.s or associate profs made the same research
The conclusion is, today it is accepted by Turkish Scholars that the age was't 9.
Because this issue is one of the biggest weapon for atheists, this question is asked nearly every TV program including a scholar, or in every religious sites. I listened from at least 5 of serious, respected scholars in Turkey that it is not 9
There are some sects in Turkey that accept this age issue as 9. But all of them, seriously all of them are ignorant about some other topics even I certainly know. So, rather than them, I choose to trust the academical ones.
Once I read a thesis paper on this issue, it was very long believe me, and it was concluding the same result. unfortunately, I don't remember the author's name.
Recently, I saw another paper written by Ayman Bin Khalid claiming that the year was actually 9. Its 38 pages old and english, rejecting all the supporting point I rely on,
I haven't read it yet, and I don't know when to read, but when I read it, if I change my mind, I will ask a professor from Presidency of R.A. about it. Then, if I change my current belief, I will write on this question and change my answer.
By the way, how can I open a chat like this with someone? I seriously don't know where to click