Luke was 19 at the time of the Battle of Yavin. That’s in Galactic Standard years, however (368 days). But those are Galactic Standard days, 43 hours of 23 minutes each. Oh, and those are Galactic Standard hours, which are 69 minutes long.
Up until just before the events of A New Hope, Palpatine had had to let the Senate think that they still ultimately controlled things; sorta the way Augustus Caesar supposedly was merely fullfilling an extraordinary mandate of the Roman Senate. The Death Star was to allow Palpatine to abolish the Senate and rule as an undisguised despot. I suspect the first Death Star had to built with the massive use of clever bookkeeping, to hide just where so many appropriations for the Imperial fleets were being diverted to.
General: We could have it done tomorrow, if money’s no object.
Darth Stewie: Uh, hmmm, uh.
General: Or we could get some estimates.
Darth Stewie: Yeah, get some estimates.
On a related issue, I’ve always wondered about how Obi-Wan Kenobi aged. We “first” see him as a young man in The Phantom Menace; he looked like this. The next time we see him is in ten years later, in Attack of the Clones, and he looks like this. Three more years pass by, and he looks like this in Revenge of the Sith. And then we skip forward another nineteen years to A New Hope, and he’s turned into this.
Obi-Wan’s about 25 in Phantom Menace; 35 in Attack of the Clones; 38 to 40 in Revenge of the Sith; and then late fifties to early sixties in A New Hope–easily enough time to go from Ewan McGregor to Alec Guinness.
Not to mention Obi-Wan, brought up to be a defender of the Republic, is partly responsible for its downfall, the nearly complete destruction of the Jedi order, and the creation of the monstrous Darth Vader, scourge of the galaxy.
It’s because of the unions… Dammit, like three people beat me to the punch.
IIRC, the one seen at the end of Ep III wasn’t the one in Ep IV. The placement of the big gun was different. I had the impression that Ep III’s Death Star was something of a proof-of-concept which would lead to production of the one in the next movie.
The unions were obviously alien-inspired-and-covertly-led organizations designed to weaken the Empire from within so that out-galaxy groups (read alien races) could invade and enslave the pseudohumans.
Professional nerd alert: By the time of Star Wars, the superlaser’s targeting system had been tested and installed on the operational platform. Since Return of the Jedi is set a few years later, there was plenty of time to develop the next version of the targeting system and field SuperLaser Targeting v3.0 (beta-2 release) at the Endor facility.
Isn’t R&D usually faster for improvements on an existing platform than it is on getting the platform itself up and running? You can figure out what adjustments need to be made for the energizing components more quickly than you can actually plan and create the energizing component itself.