Ah, the young!
It is true, that if you change your speed and/or your direction at a fast enough rate you would move ahead in time (age at a slower rate than your stationary surroundings). But in order to change your speed and/or direction (leave the inertial state), you need to apply energy. However, to change either your speed or direction at a fast enough rate to make a noticeable difference, it would take an unrealistic amount of energy. Still, it is possible, and has actually been proven in experiments involving astronauts and airplane pilots -but only to millionths or billionths of a second differences.
Why does time change?
Ever feel like time moves very quickly and sometimes very slowly? Like how the hours fly by when you're hanging out with a close friend, or how seconds drag on endlessly when you're stuck in traffic on a hot day? But you can't actually speed time up or slow it down -it always flows at the same rate, right?
Albert Einstein didn't think so. His idea was that, theoretically, the closer we come to traveling at the speed of light (186,000 miles per second), the more time would appear to slow down for us from the perspective of someone who, in relation to us, was not moving. He called the slowing of time due to motion time dilation.
Imagine you're standing on Earth holding a clock. Your friend is in a rocket zooming past you at nearly 186,000 miles per second. Your friend is also holding a clock. If you could see your friend's clock, you'd notice that it seems to be moving a lot more slowly than yours. Your friend, on the other hand, thinks the clock in the rocket is moving just fine, and it's your clock that seems to be moving more slowly. Sound confusing? Well, remember, it took Einstein years to figure this out, and he was pretty smart (see Genius Among Geniuses).
The twin paradox
Einstein came up with an example to show the effects of time dilation that he called the "twin paradox." It's a lot like the Time Traveler game you just played. Let's try it out with a pair of pretend twins, Al and Bert, both of whom are 10 years old in their highly futuristic universe.
Al's parents decide to send him to summer camp in the Alpha-3 star system, which is 25 light-years away (a light-year is the distance light travels in a year). Bert doesn't want to go and stays home on Earth. So Al sets out on his own. Wanting him to get there as quickly as possible, his parents pay extra and send him at 99.99 percent the speed of light.
The trip to the star and back takes 50 years. What happens when Al returns? His twin brother is now 60 years old, but Al is only 10 and a half. How can this be? Al was away for 50 years but only aged by half a year. Has Al just discovered the fountain of youth?
Not at all. Al's trip into space lasted only a half year for him, but on Earth 50 years passed. Does this mean that Al can live forever? Nope. He may have aged by only half a year in the time it took 50 years to pass on Earth, but he also only lived half a year. And since time can slow down but never goes backwards, there's no way he could grow younger.
http://www.pbs.org/wgbh/nova/einstein/hotsciencetwin/index.html