Time dilation happens with things in orbit. Also, the two twins have different experiences as Twin B required acceleration to get into orbit, is in a weaker gravitational field because of high altitude and has a constantly changing acceleration vector.
That is body changes and thus relative to the action only. According to the action aging could speed up or slow down. According to the action, a clock could be thrown off in its clocking of time by either advancing more quickly or more slowly.
Measure the speed of light in a vacuum at speed in orbit and it will measure the same as in a vacuum on Earth. Amazing how little understanding there is of the principle of uncertainty, of fractality, of square matrix (of eigenvector (of c^2)).
How fast are we traveling through the universe, the multiverse, at large aboard good ship Earth at 1g which varies every time we or anything else moves . . . any time that we accelerate and/or decelerate aboard it a lot or just a little bit?
Time is observed to slow down because light stretches out between objects separating and objects, including clocks, have moved out beyond observability. Time is observed to speed up because light contracts between objects closing upon one another and objects, including clocks, are still beyond observability (in the case of contraction objects being closer than observed).
When life begins breaking out into space, physicists are going to learn it isn't living any longer, or any shorter, than the normal aboard good ship Earth (given manmade created approximately equal conditions). It will still be local condition dependent and not SPACE, TIME, and particularly not SPACETIME -- as such in and throughout the universe -- dependent. A second, microcosmic and macrocosmic, will remain the same second universally for all observers, thus all travelers too, given approximately equal local-relative conditions. The twin who goes into space and has it rough there could come back to Earth having aged more than the twin who stayed home. Time, as time universal (t=0), won't be a factor. Space, as fractal, as square matrix (eigenvector) hyperspatial, won't be (in and of itself) a factor.
I'd age faster, too, than any twin I had on Earth, if I were being flattened at something like an unadulterated 10g's of local-relative acceleration or deceleration.