In TWW, the Master Sword put a seal on his magic. The OoT seal, to my knowledge, did no such thing. It simply trapped the magic that was seeping out of the Sacred Realm, and later Ganon himself.
In ALttP, he used Aghanim to "get out" and he still needed to break the seal.
It wasn't in the Sacred Realm... in ALttP.
And it's never once mentioned that it used to be in the SR. You can't use that as an explanation when there's no evidence for it, don't you get it? I could say that the Hyrule in LoZ is Koholint because Koholint existed once. It's the same thing.
I'm proposing that he escaped the seal long before ALttP.
1. On ALttP precedent it would have stayed with the King. On OoT/ALttP manual precedent it would've gone to Link, Zelda, and Ganon.
It wouldn't have stayed with the King; the King dies forever in the end of the game.
1. That's not proof, and once again you're only using some parts of canon while ignoring others.
Which canon am I ignoring?
2. That's what they mean, though. It's just more flowery language.
More flowery language that doesn't mention anything about a seal being broken, yes.
3. ALttP? I don't care if you think they're not the same Ganon, if one can do it another can.
1. But it floats up and splits the instant the King makes his wish. According to you, he wasn't dead at that time. If we go by OoT/ALttP's manual, it went to Link, Zelda, and Ganon because they were the chosen ones. If we go by ALttP it would've stayed with the King.
You said yourself the Mirror isn't in the realm in ALttP. 
It isn't in OoT, either. In ALttP's manual it is said that it didn't even become a real world until Ganondorf corrupted it. Again, it's completely baseless fanfiction which cannot be used. There's no point in theorizing if you just make up whatever shit you need for your theory.
Conversely, you're running with the assumption that it's not, and making all kinds of interpretations simply based on that.
Mine's [img]http://forums.legendsalliance.com/public/ALOT.png[/img] less worse. See above why.
There exists at least one way "around" the sages' seal, and that is the Magic Mirror, used by Link. ALttP also suggests that Ganon could not return to the light world because he "couldn't figure out how", not necessarily because he was trapped there by the seal (although the seal is what prevents him from creating his own portal back to the light world). So is there a way out of the Dark World, despite the seal? Maybe. Could someone else, OoT Ganondorf, for instance, used this other way out? Maybe. Is that other way out simply the Magic Mirror? Maybe.
Um, explain why Ganon tried to break the seal if it wasn't impeding him.
This would be what we call "interpretation", however correct or incorrect you may be.
And what you're doing is called "baselessly throwing out fact because it suits your theory".