In
Oot, Link was just a boy, and when he pulled the Master Sword out of the Pedestal, he was too young to be the Hero. So, his spirit was sealed for 7 years, and then he was old enough.
If he was too young to be the Hero, then shouldn't have WW Link be too young?
The
legend shown in WW stated that a boy in green clothing defeated the evil. The term "boy" was also used by Ganondorf when Link defeated his first form in
Oot. It might be possible that the term "boy" was taken literally and was thought to be as young as the Link in WW.
My point is that the age requirement shouldn't have changed, even if the legend passed down was talking about a boy. So, WW Link technically should have been too young to pull out the Master Sword and be the Hero. Apparently not though. Then again, there was really no Sacred Realm or Sages, so maybe this rule did not apply.
However, maybe this requirement was only for the Hero of Time?