Gravitional time dilation is actually a real phenomonon that has observational evidence here on earth. This only occurs because time is relative which means that time runs at different rates and different reference frames. This is caused because areas with a strong gravitational environment time will run slower and vise versa.
Say you are near a black hole, like the one from "intersteller" your refrence frame, or otherwise known as your perception of time, will change if say you were looking at a blackhole from earth. So lets say if you were near the black hole in space it took 30 seconds, if you were on earth looking at the black hole it would be less than 30 seconds. Therefore, you would age slower than people on earth. This is because of the stronger gravitational feild environment you're in the more extreme the time dialtion.