Get in an airplane or spaceship and go really fast for a while.
Time will slow down for you and when you land you will be in everyones future.
If you and your twin sibling were exactly the same age when you took off, then when you land you will be younger.
don't believe me? Read a book on astrophysics.
Want to ponder on something in the meantime?
If you're sitting alone in the blackness of space, just floating 'completely still', and someone comes moving toward you at a constant rate, and you pass, how do you know who was moving, or at what speed if they also said they were 'completely still'?
