While we're at the "very old stuff" thing - there was the discovery of c 12,000 year old stones with holes in them that are suspected to be spindle whorls.
The authors and their associates did some tests with replicas of the bored stones, and it was indeed deemed possible to use them for spinning, though the spinner working with them had issues spinning wool and only was content with the results spinning flax. That was, as far as I could tell from the paper, processed the modern way with retting - and whether that technique would already have been used 12,000 years ago is another question. Most of the stones weigh between 2 and 15 g, which is also quite lightweight - though that would be depending on the technique used and the spinner's preference as well as just plain physics.
In my opinion, there is no good evidence for spinning this early; the very early threads we have were spliced, not spun. I could well imagine the bored stones to be used in some context with textile production (such as twisting two spliced lenghts of fibre together, for instance), but not really for spinning.
The article itself, if you would like to read it, can be found here. And I'd be happy to hear what you think about the stones!
Agree with you that it comes under the category of "quite hypothetical". If the finds were from a culture and period where spinning was established through other lines of evidence, I'd be more inclined to believe it. However, the very low weight of the "whorls" makes it harder to attribute them as whorls, and therefore makes them much weaker as the sole evidence for spindle spinning at this date. I'm also always leery of people who make the "light whorl = fine thread, heavy whorl = thick thread" argument (especially with such very, very light whorls where the cop quickly becomes many times heavier than the whorl) and I don't really trust modern "experts" to determine whether something was a whorl or not, since their knowledge and opinions are invariably so, so coloured by the modern "drop spinning" technique.
All in all: many things can be used as a whorl, but that doesn't mean that they were a whorl.
Yes, the weight is another thing - though there are some very, very lightweight spindles that were actually used as such (if mostly with cotton, at least those that I know of) so that has lost a bit of weight as an argument in my personal universe.
But yes, if someone goes to the very simplified "spindle weight equals thread thickness", my alarms start sounding as well.
The "many things" does sum it up well...