You would age the same amount during deceleration that you did during acceleration.
I think your misunderstanding comes from the relativistic twin paradox.
From the perspective of the twin on the spaceship accelerating away from earth, the twin on earth seems to age slowly as well until the space ship twin decelerates and then turns around, during which they perceive the twin on earth to age rapidly.
The acceleration / deceleration of the space ship twin’s frame of reference is what breaks the symmetry of the no-preferred frame of reference during flight.
I think your misunderstanding comes from the relativistic twin paradox.
From the perspective of the twin on the spaceship accelerating away from earth, the twin on earth seems to age slowly as well until the space ship twin decelerates and then turns around, during which they perceive the twin on earth to age rapidly.
The acceleration / deceleration of the space ship twin’s frame of reference is what breaks the symmetry of the no-preferred frame of reference during flight.