Let's say you took a trip to Alpha Centauri, about 4 light years away, going 90% the speed of light all the way there and back (we'll pretend you don't need to accelerate and decelerate). To observers on Earth, about 8.8 years would have passed before you return. However, from your perspective, only about 3.8 years would have passed. Your biological age would have increased by 5 years less than everybody else, though each person would feel as though time had passed normally for them.

Edit: as a side note, if you could travel at 99.9999% the speed of light, you could get to the center of the Milky Way galaxy and back within a typical human lifetime. Of course, back on Earth more than 50,000 years would have passed and humanity might not be here anymore.