The Twin's paradox is a well known paradox in which there is a difference in the ages of twins after one twin travels a round trip around the space and returns back while the other twin stays put. I understood how the gap in their ages arises because of the finite acceleration time taken during the change of velocity while the travelling twin takes a turn. But my question is, when he starts decelerating/ accelerating, won't he observe the other twin decelerating/ accelerating too? I mean, if I'm accelerating away from a reference position, that point will also accelerate in the opposite direction in my frame, right? I searched the internet for relevant answers to this question to which I didn't find anything concrete. Any help is appreciated. Thanks.
The central thing you're missing here is that you can tell when you're in an accelerating frame.
If one twin notices that objects that aren't tied down begin to accelerate without being acted upon by any forces, then he knows that he is in a non-inertial frame, and that his observation that the other twin is accelerating is due to his own acceleration.