What causes people to age differently?

What causes people to age differently?

Here is a simple example:

A man moves inertially between two clocks in inertial coordinate

system A. He is age 20 when he starts.



Man

(20) -->

[0]-------------Frame A-----------[?]

Clock````````````````````````Clock



Man

---------------------------------(23.67) -->

[?]-------------Frame A----------[3.80]

Clock```````````````````````` Clock



The A-frame observers note that his aging rate is 96.47 percent

compared to the observers' clock times.



A second man moves faster but still inertially between the same two

clocks in inertial coordinate system A. He is also age 20 when he

starts.



Man

(20) -->

[0]-------------Frame A-----------[?]

Clock`````````````````````````Clock



Man

---------------------------------(21.37) -->

[?]-------------Frame A----------[1.70]

Clock`````````````````````````Clock



The A-frame observers note that his aging rate is only 80.87 percent

compared to the observers' clock times.



The question is What causes the men age differently? I know that

the math gives it, but what is the physics behind the math?

(Remember the epicycles!)

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