Reading about the speed of light on Wikipedia.

Since one might not travel faster than light, one might conclude that a human can never travel further from the earth than 40 light-years if the traveler is active between the age of 20 and 60. A traveler would then never be able to reach more than the very few star systems which exist within the limit of 20-40 light-years from the Earth. This is a mistaken conclusion; due to time dilation, the traveler can travel thousands of light-years during his 40 active years. If the spaceship accelerates at a constant 1 g (in its own changing frame of reference), it will, after 354 days, reach speeds a little under the speed of light (for an observer on Earth), and time dilation will increase his lifespan to thousands of Earth years, seen from the reference system of the Solar System, but the traveler’s subjective lifespan will not thereby change. If the traveler returns to the Earth, he will land thousands of years into the future.