Why Do We Age Slower In Space ?

In the movie superman there is a famous scene where the man of steel spins round and round the planet to turn back time.
While the idea is pure comic book fiction, if someone was to spin round the planet it would indeed effect time but just for them. Time is relative which means that the rate at time passes changes based on numerous factors such as gravity or how fast you are moving. What this is means is that astronauts up in space are aging slower than everyone here on Earth, but why ?

Einstein's theory of relativity created the idea that there is a fabric that spread throughout the whole universe called space-time. Space-time does not stay same. It can be warped by matter and energy, this is called time dilation.
Time moves slower on Earth than it does in space because the Earth's gravitational force bends space-time. This is gravitational time dilation.

If you were out in space away from Earth's gravitational pull you would age faster than someone back home. As gravity is stronger the closer you are to the surface it means your feet are younger than your head and a person who lives on the ground would age slower than someone who lived at the top of a mountain but the difference would be so tiny as to make it imperceptible.
Time also moves slower the faster you are moving. This is called velocity time dilation. In the twin scenario, if one twin remained on Earth while the other twin flew off in a rocket around space before coming back. The twin in the rocket would find upon returning that their earthbound twin had aged more. This is exactly what happens when you have an atomic clock flying around in an airplane. It will record less time as having passed than an atomic clock that stays on the ground. So do we age slower in space or not ?
The answer depends on what you are doing in space. If you were floating in space above Earth and not moving, you would age quicker. But for those astronauts on the ISS which whizzes around Earth at about five miles per second, they would actually age slower because their velocity time dilation has a bigger effect than their gravitational time dilation. A six month stint abroad the ISS would give you about 0.07 seconds of extra life. So if you want to stay young relative to other people on Earth all you have to do is find a way to spin round and round the planet at incredible speed just like superman.