At vero eos et accusamus et iusto odio dignissimos ducimus qui blanditiis praesentium voluptatum deleniti atque corrupti quos dolores et quas molestias excepturi sint occaecati cupiditate non provident, similique sunt in culpa qui officia deserunt mollitia animi, id est laborum et dolorum fuga. Et harum quidem rerum facilis est et expedita distinctio. Nam libero tempore, cum soluta nobis est eligendi optio cumque nihil impedit quo minus id quod maxime placeat facere possimus, omnis voluptas assumenda est, omnis dolor repellendus. Itaque earum rerum hic tenetur a sapiente delectus, ut aut reiciendis voluptatibus maiores alias consequatur aut perferendis doloribus asperiores repellat.
your question is related to the famous twin paradox, and time dilation
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
oops.. both persons...
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: |dw:1437248921806:dw| the person in S sees the person in S' who travels at a speed near to the light speed
the person is S' measures his time say t' whereas the other person in S measures his time t
so we have two different times
and, we have: t' < t
namely: the person in S' ages more slowly than the person in S