I believe Miyamoto mentioned something along those lines a very long time ago....I think that was even
before we learned what we did of Skyward Sword at
last year's E3. I think he said this back when we only had that single concept art image of Link and Phi/Fi. At that time, I think a lot of the details hadn't been refined, and in fact, we all know that since that time, Miyamoto had upended the teatable and switch art directions. I think when they did this, they might have opted to have a younger incarnation of Link than they were originally thinking.
While not by a huge ton, I feel Link seems to have taken on a younger look since then:
Therefore, while I do believe Miyamoto said that at some point, I think what we see of Link now suggests that Miyamoto has changed his mind since then, probably in conjunction with when he changed the direction of the art style.
So, unless Miyamoto sends out new comfirmation that Link is indeed the oldest, I'm not so sure I'd believe it anymore.