It's called 'Relativity' because of the
Principle of Relativity - which "
requires physical laws to be the same for any body moving at constant velocity as they are for a body at rest (relative to some observer). A consequence is that an observer in an inertial reference frame cannot determine an absolute speed or direction of travel in space, and may only speak of speed or direction relative to some other object."
The reason that there is an age difference at their reunion is because one twin has changed his inertial frame at the point he turned around to come back; this makes a significant difference, as explained in this
Minute Physics video:
That is so much pseudoscience it isn’t even funny. I mean please, we have observed clocks slowing aboard airplanes, and they certainly needed no frame switching at their turn around point to do so. It was changes in velocity, and changes in velocity alone which caused those clocks to slow. You don’t even understand the actual experiments performed, instead spout pseudoscience touted long before any actual experiments were performed.
And no the laws are not the same, except for observers moving at the same relative velocity.
“Special principle of relativity: If a system of coordinates K is chosen so that, in relation to it, physical laws hold good in their simplest form, the same laws hold good in relation to any other system of coordinates K' moving in uniform translation relatively to K.”
Only if the systems are moving in relative motion with respect to one another do the laws of physics hold good. Your understanding of relativity is flawed.
“The laws of motion in non-inertial frames do not take the simple form they do in inertial frames, and the laws vary from frame to frame depending on the acceleration.“
Your belief holds no merit, only when two observers move in relative motion (the same approximate velocity) in an inertial frame, do the laws of physics hold good in both frames. In a non-inertial frame the laws vary depending upon the acceleration.
Hence clocks slow as well as decay rates under acceleration. Their is no pseudoscience of switching frames at turn around, as explicit empirical tests performed in airplanes have shown. It is changes in velocity, and changes in velocity alone which cause clocks to slow.
And least understand Relativity before you make claims you can’t support.