All this talk about time-dilation led me to produce the following chart which clearly demonstrates one of the difficulties of space travel at relativistic speeds between 0.5c and 0.995c.
(Assuming you wish to be able to renew relationships on your return.)
This shows the approximate ages of the 2 twins after one twin returns from a round-trip non-stop voyage to Alpha-Centauri at various fractions of light-speed. (after departing at the age of 20)
twins_alpha.PNG [ 27.56 KiB | Viewed 1304 times ]
Based on the time-dilation formula:
bigeq.gif [ 2.26 KiB | Viewed 1303 times ]