You are mistaken, time travel is posible, and we arleady know how to do it, but at this time, we are unable to.
If you travel at the speed of light, it distorts time, with out going into the details to deep, if a "space ship" travels at the speed of light to and from a destination, it affects the time line, when the ship returns, it would find that everyone else has aged by a certain amount of years, while anyone on the ship, would have aged slower.
This has already been proven with the Space shuttle, as it travels some where around 20K to 35K mph. All clocks/watches on the shuttle, differ from the clocks on earth. Only by a small amount, but it still differs. Once we come up with a new form of fuel/matter to propel such ships further out into space, the difference will only increase, and time will be altered in such a way that those on the ship, will age different than those still on earth.
How's that for deep.
If you don't believe me, Google it, and I'm sure you will find what I'm talking about. I say a special on just such a thing on Discovery Channel where they covered all sorts of things, like black holes, worm holes, and time travel.