Question

a

Answer 1

your question is related to the famous twin paradox, and time dilation

Answer 2

please, see my tutorial on Special Relativity, for more details, about the time dilation:
http://openstudy.com/study#/updates/55959d90e4b01def59ee5ca3

Answer 3

in few words, for a person who travels to a speed near to the light speed, his time runs slowly, with respect to the time measured by a person at rest. Please note that both person measure the time in the proper reference system

Answer 4

oops.. both persons...

Answer 5

we have 2 reference systems:
one is the reference system at which the persons who travels at a speed near to the light speed is a t rest, and
the other is the reference system with respect to the first reference system is moving, namley here is my drawing:

the person in S sees the person in S' who travels at a speed near to the light speed

Answer 6

the person is S' measures his time say t'
whereas the other person in S measures his time t

Answer 7

so we have two different times

Answer 8

and, we have:
t' < t

Answer 9

namely:
the person in S' ages more slowly than the person in S

Answer 10

ok!