I'm sorry if my tone comes across in an arrogant way. In general I think I'm quite good at writing and understanding English, but I have no clue how my tone sounds like. I apologize.
Still I find it quite bothering that people (Alberto) keep telling me that I have no clue, that I should "study more" or "take my old physics books from the shelf - too long time has elapsed". Speaking of arrogant, stuff like "at 14 years old my main interest was soccer" is very helpful to keep arguments on an objective level.
I always try to give explanations, but what might sound clear to me might not be clear at all to others. Then ask. But I often have a feeling that posts are not read carefully and stuff is said only that something is said. I mean, we've already resolved the twin paradox like twenty posts ago and suddenly the discussion starts all over. In threads like these that's annoying. I spend quite a bit of time writing my posts, looking up stuff etc., but I don't see any sense in it if you're not interested. I could as well do other things.

So much for that. To repeat my arguments referring to the twin paradox let's look at it in a different way.

• Horizontal lines mean "at the same time" for A
• Red and blue lines mean "at the same time" for B
• Points mean proper time
• During flight, A thinks that B is aging slower while B thinks that A is aging slower (check that in the diagram, when B reaches point B he has passed 4 years proper time during which A has aged about 3.2 years - and vice versa)
• When B turns around - however that is acheived - A ages rapidly when seen from frame B
• This is what distinguishes both frames: while B ages slower all the time when viewed from A, A ages slower in frame B only while B is flying
• Both frames are clearly distinguishable
• There is no question whom of both will be older at the end
• No gravity involved whatsoever
• This effect is only due to the change of inertial systems of B

To calculate it with a cheap trick which completely obscures the physics behind it imagine that B travels for, say, ten years as seen from frame A and then beams back to earth. Of course his proper time is shorter than the time on earth (t/\gamma). As seen from frame B this picture is complete nonsense, though.