Bastion/WMG

The Kid's Age

Rucks states that the Kid joined the military because "School ain't workin' out." Assuming shared school-ages between Earth and Caeldonia, he would drop out of highschool (age 17), opt out of college (age 18-19), or drop out of college (19-20). That gives us a four-year age-range. After his five-year tour (I think it was five), that puts him at 22-25 years old. His second tour was interupted by the Calamity, which gives us a range of 0-5 additional years, but more likely 1-4 (at least one full year served and at least one full year left). This give us a final range of 23-29, not a child by any means, but still young enough that fifty-or-sixty-something Rucks would be justified calling him "Kid."

My guess is high-school drop-out, serving a four-year second tour. 17 + 5 + 4 = 26
I'm going to go with a younger age, the world of Bastion seems to be in the industrial age, where it is not uncommon for a kid at the age of 12 to leave school. Give him 9 years of service, that puts him at 21 for the game, plenty young to be called "Kid."
- That was how I took it, too...but I figured he'd spent closer to a year or two into his second tour of duty, making him more like 19, tops.

The Bastion never has enough power to rewind time far enough.

While it's not explicit, when starting a New Game+, Rucks' last words to the Kid at the end of the game are heard, right before the narration starts at the very beginning with the Kid waking up.

This could easily suggest that while The Bastion's true function actually works, its intent fails miserably, both in that it will never be able to truly erase the Calamity and that there is no way to inform the past of this fact, causing a recursive loop until someone like Zia breaks it.

Or, due to Zulf's destroying of the monument, the Kid's failure to get a few cores and shards, and the Ura's attacks on it The Bastion will never have to send the survivors all the way back into the past before the calamity. Even in New game +, Rucks will make comments about already saying things or having dejavu on saying them, so the memory function is at least partly functional just like the time travel part, sadly they will never enough power to go back far enough, and thus be stuck in the loop till the kid breaks it.

Rucks is related to the Kid in some way

Possibly even his father. Both have white hair, even though Ruck's could be from age it seems to be implied that white hair is unusual in Caelondia as both the Kid and his mother were ostracized for it. Also how coincidental is it that the man who created the Rippling walls, The Bastion, and helped create the Calamity is alive and so is this one other guy who happens to have the city crest which is somehow connected to the Bastions Reset Button function.

However, Rucks is old enough to have come by his white hair honestly.
And we're specifically told that "everybody on official business for the City carries the Star of Caelondia," so that's not so useful.
- The question then becomes, since the Crest protected The Kid, and probably causes the "land forming under his feet" effect ("there's a bit of the Bastion's power in the Crest," Rucks tells us), why didn't anybody else's Crest work like that?
  - The Kid survived because he was scouting the outer edges of the Wall, not because of the crest. Zia and Zulf survive because they sheltered in Ura Dens. Only Rucks' survival is unexplained in the game. Presumably, anyone's crest would work, as long as they survived the Calamity.
  - Rucks was able to survive due to already being at the bastion before the calamity happened. The restoration ending which shows the survivors what they were doing before the calamity, shows him next to the monument.

Somewhat related: the first time I heard about the Bastion's time travel powers, I almost immediately thought Rucks would turn out to be Kid himself, stuck in a time loop.

All replays are canon

One of the endings allows you to rewind time to before the Calamity. With this, every time somebody plays the game can be canon, and all cases of New Game Plus are simply a sign that things happened differently before the Calamity.

The Kid is the son of Asura

White hair, uncanny determination and battle dialogue composed almost entirely of enraged grunts.

The "reverse time" ending goes first, then the "evacuation" ending on the New Game Plus

At first, the Kid thinks it would be a great idea to restore time to before the Calamity. When he finds out this doesn't work, he decides to go along with evacuating everyone, since it's the best option for everyone. Besides, the Kid keeps a lot of stuff on the New Game+, but no one else can remember a thing. He clearly knows a lot more that it looks like.

After all, the player is sure to pick up that the reset didn't work and since he's an extension of the player...
Heck, even without the Kid remembering, it's clear that some variables are randomized since everything doesn't go exactly the same. Provided there was any chance at all of him choosing the second option, do that enough times and you're bound to get it eventually.

There are other tribes of people out there in the world who survived.

The Kid, Rucks and co. will link up with them after they evacuate the Bastion. Though this is more of the optimist in me speaking than anything from the game.

Don't be so negative about that - After all, the background during the Evacuation ending shows the party sailing, Sky Pirate style, towards a small town on the edge of a large, probably solid landmass. Personally, I think that they fly the Bastion back to the Cael homeland. Set their sails and fly back to home, sweet home, and then dock that thing right on their doorstep, so to speak.
Not to mention that hey, an awful lot of Ura survived the Calamity and it was specifically designed to kill all of them. Granted, they did this by burrowing underground, but surely some people farther from Caledonia would do even better.
Also, it should be noted that the Calamity is specifically described to only have targeted Ura, with Caelondia added in at the last minute. Assuming that these aren't the only two countries in the world, then presumably the rest of the world is untouched by the Calamity.
It's almost explicitly stated that Caelondia is a colony, presumably on a different colony then the Cael homeland. Since distances are never mentioned, and the only other city (If it can be called that) Kid visits is the Tazal Terminals, it seems fairly reasonable that only a (relatively) small area of the world was affected. After all, the Calamity gun was just a weapon of mass destruction, not a full-fledged doomsday weapon.

Zia planned to betray the Bastion to the Ura survivors, while Zulf was completly sincere

Think about it; The game pretty much spells out Zulf was a diplomat, so making friends with Caelondians was his job. He most likely planned to get back in touch with the rest (now that he was no longer forced to stay) and broker a peace deal between the survivors. When he found the journal and found out what cause the calamity he was pissed off and tried to restart the war instead.

Meanwhile think about Zia's motives; before the calamity every Caelondian she knew either mistrusted her, played with her feelings and stabbed her in the back or otherwise gave her nothing but Fantastic Racism. While it's possible she didn't hold a grudge (since she was culturally Caelondian anyway), keep in mind that her song/theme is basically (well, see my next WMG, but still) a threat aimed at Caelondia from the Ura. Therefore it's possible that when she slipped away to investigate what Zulf told her, she disgarded her harp for being Caelondian, met the other Ura with the intention of betraying The Kid and Rucks to them, realised that they were still jerkasses (given how well their meeting went) and decided to side with The Kid when he turned up to rescue her.

The song Zia sings actually a lot less warlike than it sounds.

Reading the lyrics it sounds a lot like a threat from the Ura to Caelondia. However when you think about the double meanings in the other songs with lyrics ( Zulf's theme is about going home while he's slowly dying, however it also echos The Kid returning home to finding his mother had died and someone had simply pocketed the money he sent back, Coming Home has the going back in time business and The Pantheon is both Rucks having a Rage At The Heavens and lamenting his own mistakes) it could just as easily be a warning (after all, if the Ura had religious beliefs against living above ground and they were on good enough terms to send a diplomat they might be inclined to "warn" the Caelondians. It could also imply an intention to build stronger ties; "So build that wall and build it strong/'Cause we'll be there before too long" could mean "Make sure you're well defended, because we're going to attack" or it could mean "make sure you've got some good housing sorted out for when we join you".

Rucks is actually the Kid.

He seems to be the only one to have partial memory of the events occurring, and tells the full story to Zia, even parts that he probably wouldn't have heard otherwise. Because of the damage to the Bastion, instead of sending back all of the occupants with their memories intact, only the Kid (the one who pulled the switch) makes it back to Caelondia about twenty or thirty years before the Calamity. They dress nearly the same, they have the same hair and (from what I can tell) eye color, and Rucks seems to be vaguely aware of the workings of the time loop caused by restoration.

Wait a minute. If The Kid gets preserved in each Restoration, how did we end up with two? Also, Rucks advises The Kid in the game... if he knew that much, wouldn't he have fixed the problem when he was still young enough to get around?

The Kid is Roland Deschain.

Based solely on the Groundhog Day Loop nature of the game's plot, and the fact that the kid can equip himself with some badass revolvers. There's not enough evidence otherwise; this theory just seems rather cool.

Alternately, The Kid is Arthur Eld.

Rucks wasn't lying about his careers.

He's at least 20 years older than the other 3 main characters. So who says one can't move up the ranks of an organization? Maybe the reason no one expects someone to take multiple tours of duty as a Mason is because they expect you to either retire or change career paths. He could have started as a Mason, moved up to being a Trigger and obviously ended a Mancer.

- When choosing the Cael Hammer/Army Rifle combo he comments that this is his own favourite set from the past. Given that both weapons seem to be EXCLUSIVE for a particular guild (The Masons and Triggers respectively) it's possible that he worked his turn on the Walls, then enrolled into the Army.
  - But Rucks also designed the Walls. Which is kind of weird since he was a soldier in the war yet was already engineering major infrastructure for the city, and that's if we avoid how old he'd have to be then.

Rucks knows Cave Johnson

Because I have added this moment of epicness to my own personal canon.

Caelondia eventually becomes the city of Oneiros, seen in Clive Barker's Undying

Think about it. Both were once magnificent cities destroyed by a mysterious disaster, and remain as chunks of masonry floating in an infinite void. Both also feature pieces of land spinning up to form walkways for the player's convenience. Sure, Oneiros looks a lot more decrepit, but that's because it's been in such a state for so much longer.