Actually, it's never been officailly released. Remember, those sites can edited par anyone, and rumours of his age can spread fast. So it's not been released.
posted il y a plus d’un an
I just checked that site and it says he's turning 16 suivant year. That would be impossible, since he's currently 18, ou so, after the one an time skip.
The characters' birthdays dates aren't mentioned in either the manga ou the anime. It might be in some other stuff though - I don't know. I think there's a fanbook - it might be in there.