I'm curious why it is a few years before a student is ready to select their first weapon. It seems to me (from an entirely uninformed viewpoint) that a student should be informed enough after maybe a year to select a sturdy, inexpensive weapon with the advice of their instructor.
Hmm... not exactly what I'm getting at here....
It's often expected that a new student in Iaido gets their own Iaito as soon as they can afford it (once ensuring that they are interested enough to drop the cash on one, of course), but that's not what is being discussed in the website, or in PhotonGuy's series of threads. And, yes, of course it's expected that the student consults with the teacher... who will offer advice on size, preferred manufacturers/suppliers (if they have any), and anything that would not be considered "acceptable"...
The real point, of course, is that we're not talking about buying an Iaito (a zinc/aluminium alloy blade, unsharpened and unable to be sharpened, used as a safe substitute to a sharp steel one), as the website is about buying "katanas" (sic)... namely, sharpened blades. PhotonGuy is in no need of anything like that... typically many Iaidoka use Shinken (live blades) from Sandan onwards... and, even if his group is doing tameshigiri regularly, most likely his dojo would have a few "dojo cutters" to be used... ones that have been vetted by the instructor already.
When it comes to why a few years, for one thing, it can take time to develop the sensitivity and awareness of the differences (which can be fairly subtle to begin with) between something that is good, and something that borders more on unusable... especially in something like Iai, where you're spending many hours drawing and cutting, then resheathing the weapon (with many single hand actions)... so a weapon that's poorly balanced, or too heavy, or too light, can lead to strain and injury, as well as issues with technique and performance. Figuring out what precisely is "your requirement" for a frequently used item can take a while.
Is some of the process a holdover from the time when (IIRC) training for a sword would start quite early, so there would be no need to get around to the individual's own weapon until they had some years in (and were approaching fully grown)?
Uh, no, really. On a few levels.
Just a guess here, but if you figure an hour or two of training, two to three times a week... We're looking at around 100, 150 hours of training in a year. How much of that is going to be aimed at selecting a weapon or the qualities versus ingraining and reshaping movement patterns?
Well, the act of training the waza acclimatises the student to the feel of a sword... getting them used to the correct way it should feel... behave... act... which is more important than if the fittings are made of sterling silver or just brass... which is the biggest issue I have with the "review" site... it seemed to focus entirely on aspects that are less relevant, and missed entirely any of the important realities of the items being reviewed. But, importantly, things such as preferences on tsuba, saya, sageo, menuki, and so on are really just aesthetic and personal choice... they make little difference... the important facets of selecting a sword are quite different, and require a fair amount of familiarity with using the weapons in the first place.
It also may not be "ready and able to select a live blade so much as ready to use one... I think a lot depends on what I guess we can call the level of sophistication of the style, as well. Some styles aren't that complicated, and can be absorbed more quickly or even get into live weapons much earlier. The long sword systems I've been exposed to aren't all that sophisticated; the basic qualities of a sound blade are pretty simple and consistent. You can pick the principles up relatively easily. I know a lot of the Japanese sword arts are much more intricate...
Hmm... I get where you're coming from, but I don't think that's overly a factor... sure, it's hoped that by the time you get a live blade you aren't about to take your own fingers off... but if you do, eh, they're your fingers...
But I'm really just speculating. Hopefully, someone with better experience can fill us in...
Ha, hope this helped!