The wiki entry (if that's where you got your info from) has always been incorrect.
He was at a French side but released and went on trial with several English sides including ourselves (I recall Birmingham City as another). He was never announced by Spurs as a signing so not sure we know the actual date (not that unusual for a youth signing), but he was certainly playing for Spurs for longer than a normal triallists which is why I'm sure he had signed for Spurs.
Wiki and other sources have simply taken the start of the first season after he signed as 'date of signing' just because its the first date they can be certain of.
BTW look at the Parrott situation for comparison - very fuzzy from the time he left Belvadere (Dublin) to signing for Spurs which I think is to go with FIFA rules on tapping up youngsters. I'm pretty sure we 'officially' signed him on his 16th birthday, although he left Belvadere the preceding 30 June (lots of Irish comment to the effect he had left there and joined Spurs) so a gap in time of about 7 months….
Applying the same logic as Parrott to Bentaleb signing on his 16th birthday (first date to legally sign a scholarship contract) or 17th birthday (first date to sign a pro contract), he would have signed in November 2010 or November 2011, although I'm sure he was playing for quite a few months for us before November 2011