A is younger than B according to the B time
is correct if Twin B would be moving in one direction at the same velocity forever. But the essence of the twin-paradox is that he's not, he went back, accelerated and thus "changed inertial frames".
Summing up
There are two twins A and , 20 years old
A remains on the earth
B leaves with his stracraft, travelling at 90 % of the light speed
B is back on the earth, 20 years later, according to the A calender
A is now 40 years old
According to the special relativity
B is only 20 + 8.71 = 28.71 years old
Therefore A will likely die first
You say (If I understood ) :
Nope B is also 40 years old because also the acceleration and deceleration must be also taken in consideration
In other words , in your opinion, there is a sort of compensation
It is right that you should consider also the acceleration for an accurate calculation of B age but the result is :
Actually B would be even younger than 28.7 years
If you have a look at the B calendar, the one hang on the starcraft , you will see that 8.71 years ( or less) have elapsed from the departure (The B time)
It seems unbelievable but it is the plain truth
The decay time ( the life spam ) of atomic particles in particle accelerator
comply with the theory
If this is true for a single particle there is no reason to doubt that it must be true also for a human being
