Incredible that he wrote that in 1908 & yet during my studies, at good schools, the "paradoxes" of special relativity were presented as paradoxes - the twins! One accelerates & that is why they are younger - true! But an impairing & opaque way of learning the lessons of special relativity...

Yes. That why I use a an analogy by now rotating on a sphere elongates or shrinks the values of coordinates, even though noting changes, to show the fallacy of such paradoxes. Though this makes it no less hard to imagine or truly comprehend it. The drawbacks of being sluggish creatures.