The concept of time dilation, as described by the theory of relativity, is indeed a real phenomenon. Time dilation occurs when an object or person is moving at speeds close to the speed of light or in the presence of strong gravitational fields. In such cases, time appears to pass more slowly for the moving object or person compared to a stationary observer.
However, while time dilation can slow down the aging process for someone in motion relative to an observer, it does not allow for "extending" one's lifespan in a practical sense. From the perspective of the moving individual, their own subjective experience of time remains the same. They would not feel as though they are aging more slowly. It is only when they return to the reference frame of the stationary observer that the difference in elapsed time becomes apparent.
Interstellar travel is a complex and challenging endeavor that involves vast distances and timeframes. Time dilation can have an effect on the duration of a space journey, but it alone is not sufficient to make such travel feasible. Other factors, such as propulsion systems capable of achieving high speeds, efficient energy sources, life support systems, and shielding from radiation, are crucial considerations. Additionally, the effects of prolonged exposure to the space environment, such as microgravity and cosmic radiation, pose significant health risks that need to be addressed for long-duration space travel.
While time dilation is a fascinating aspect of relativity, practical interstellar travel would require breakthroughs in various scientific and technological domains, going beyond the effects of time dilation alone.