You still dont grasp the principle of symmetry

B is younger than A according to the A time
A is younger than B according to the B time

In other words
Should the twin on earth (A) reaches his brother (B) on board on the star ship then he would find that his brother is older than him

Anyway I was right to suppose that some people assume that the twin paradx is a... paradox
Nope it is not

The ultimate confirmation of the theory of relativity came from the spatial missions
Before that , a minority of great scientists still believed that the relativism of time was, so to speak, a sort of mathematical trick

I quote by heart

A shuttle remained in the space about 1 year time, travelling at an average speed v = 40.000 km/hour
On return on the earth the clocks on board were t = 3.6 sec late , in compliance with the theory
So the astronauts (if any) were 3.6 sec younger according to the earth time

I would suggest to read the Bertrand Russel's book
It was written before the spatial mssions
Russel said that only the future spatial mission can tell the last word on this question

The last word was : Time is actually relative