I think I'll break from the Sages series to bring you Rauru.  It's not too much of a break, seeing as he is a sage.  But what makes him special, you ask.  Well, there's a few things about this guy that just don't make sense.  He is the only sage you do not meet as a child.  He seems to have more power than most of the sages.  Also, he didn't need to be awakened, or so it seems.  What's with him?
    
One quote from Ocarina of Time could bring us a lot of info about this guy.  He says this not long after you wake up as an adult.  "I am Rauru, one of the ancient Sages.  Ages ago, we ancient Sages built the Temple of Time to protect the entrance to the Sacred Realm."  What???  How could he be one of the ancient sages?  Now the arguments against this are obvious and can be boiled down to one statement: he would be too old.  But let us examine that closely.  If we are to assume that this statement is true, then he must have gotten around that aspect somehow.  Keep in mind that he was very powerful, and probably had some access to the Triforce.  Think back to AoL.  The old man who gaurded the Triforce stayed alive for a long time.  Perhaps they used the Triforce to halt their aging?  After all, Ganon did not age.  But I think there is a better way.  What if Rauru created a sleeping spell on himself, to be broken only when someone enters the Sacred Realm.  We have evidence of spells lasting throughout time in many places.  And this makes more sense then the no aging idea.  Wouldn't Rauru be bored sitting around in the Sacred Realm for years?
    
So, he fell asleep in the Sacred Realm.  This also makes sense from another perspective.  He never appeared in Hyrule when Link was a child.  He probably lived in the Sacred Realm.  If so, how did he get there?  He had to be from the time when Sages built the seal.  Now the question is why.  Why did Rauru accept a possibly never ending sleep?  Probably for the same reason Kaepora accepted becoming an owl: protection of the Triforce.  He could not be sure that the spell to awaken sages would work.  He also planned to be there when the bearer took the Triforce.  That way, he could prepare the bearer for his task.  He was the link to the past (yes, the pun was intended) that would provide the most help, for he could not be sure of the oter sages' motives.  And I will add a selfish reason as well.  The latter portion of his pre-sleep life was centered around the Triforce.  He was certainly unhappy to see it go.  But by volunteering to join it in the Realm, he could be awake when it would be used again.
    
Now let me try to explain what happened in the Sacred Realm when Ganondorf and Link entered.  It is unclear how Link fell asleep, but it must have happened immediately.  Ganondorf probably did not kill him immediately because his mind was on the Triforce.  But did Ganondorf and Rauru meet?  Most likely yes.  I said and still claim that Rauru would be awakened when the seal is broken.  He probably eagerly went to meet the bearer of the Triforce, but was surprised to see a little boy and an evil man instead.  There may have been some dispute, but I doubt Rauru would have had much fighting ability.  As a result, any battle that took place would have been short, with Ganondorf eagerly leaving Rauru for the Triforce.  He probably did not think of Rauru as a powerful man after that.  Instead of a direct confrontation, Rauru took Link to the chamber of Sages and sealed it against Ganondorf.  Ganondorf, not being used to the Triforce, could not enter.  There, Rauru waited until Link woke up.  He feared that the awakening call could not go out because of the evil influence.  Thus, after Link woke up, they needed a plan.  Link would fight his way to each of the sages.  When he got to them, Rauru would transfer them to the Sacred Realm, where the sage could be awakened.  Thus, it was probably a good thing that Rauru decided to stay with the Triforce.
    
Now to some it up.  Rauru was one of the original sages.  After the problem with the prince and the evil wizard, they decided that there should be a seal on the Sacred Realm.  For further protection, Rauru volunteered to stay in the Sacred Realm.  There he slept until OoT.  He tried to stop Ganondorf, but couodn't.  Instead, he protected Link and himself from the evils of Ganondorf.  With Link's awakening (I should stop, shouldn't I), Rauru worked to transport the other sages to the Sacred Realm, where they could be awakened.  After Link won, he presumably took on the traditional role of a sage and died from old age.  There was no need to have another sleeping spell.  I hope this helps.  Any questions or comments are more than welcome.