Time is one of the most mysterious object in this universe ,no one found it or may find it, time is like everywhere in the universe ,its like even in human species head ,if one belives in the concept of GOD may be he/she/it could control, speed up or slow down or even stop time ! As per Einstein time exsists like space everywhere ,in the present that means past and future also exsist concurrently ,which means somewhere our ancestors are still there and descendants also there at the present time !!Time changes with speed what we call dilation as per einstein physics !! Time Changes with speed of travelling .The faster one travels slower the time becomes and much much faster than light one travels then time becomes faster!
Einstein proved if one could travel faster and much much faster then speed of light one could travel back in time time !But the limitation is the speed of light !If speed of light is crossed then it possible travel back in time ! Rocket to travel faster than light ,yes then one may travel back in time !!
The rule Einstein shattered of Newton was that static time which is linear ,what Einstein proved is that time in not linear but it bends ! So one assumption is that if its made like swirl ( take a stick and move it cirucular motion in a bucket of water ) then it allows the dilation and excitation at the same time !!
If one travels ahead in time and comebacks they would have oldered ,if one could travel back in time and if they comeback to present they would have become younger !!