I started a thread previously (https://www.physicsforums.com/threads/time-dilation-happens-on-moving-frame-but-which-one.814622/) around this concept but it got closed by one of the staff after helpfully pointing me to http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_spacetime.html. I read that link and it does nicely explain how Stella's elapsed "proper" time is lesser when analysed using the lens of Minkowski spacetime, from the frame of reference of Terrence (assuming Terrence is at rest). But suppose if we do the same calculation from the frame of reference of Stella (assuming Stella is at rest), wouldnt we get different worldlines? Infact the worldlines will switch between them. So from Stella's frame of reference, she will calculate that the elapsed "proper time" of Terrence is less than Stella and he would have aged less. So as I see it the paradox isnt avoided and infact reinforced by this elaborate calculation. What am i missing?