Time is a peculiar thing, our perception of its length without any event to gauge it by is quite variable. Try sitting down in front of a clock for 15 minutes and watch it increment up and then try having a conversation with someone and take along your trusty timer with an alarm and I guarantee you, watching the hands move will seem so much longer.
If you are familiar with physics general relativity, you know that if you have a twin and the twin remains on earth and you jump in a rocket traveling at the speed that the Large Hadron Collider (LHC), the newest particle accelerator which is 0.999999991 times the speed of light (186,282 miles per second) around the earth for a year then when you land your rocket in your twins's driveway he will have aged a year however you will only be less than an hour older.
At this point I need to reference a verse in the Bible, 2 Peter 3:8 which states "But do not let this one fact escape your notice, beloved, that with the Lord one day is like a thousand years, and a thousand years like one day". Today, this seems extremely plausible due to the nature of relativity and time.
The energy for the LHC to accelerate particles to 0.999999991 times the speed of light (186,282 miles per second) is 13 TEV (trillion electron volts). Should one of the containment magnets fail, it would blast a hole through the walls and more than 100 meters through the earth adjoining it. We cannot produce the energy to push John's rocket to that speed so that will not be happening anytime soon.