My how time flies. Isn't it something how twenty years ago seems like only yesterday, yet back when you were four, a summer lasted for a small eternity? Not only have we all heard this sort of thing, but every last one of us experiences time exactly this way. Meanwhile, we have the clock ticking away at exactly the same rate today that it ticked forty years ago. The reason that this can happen is because there is no real time which exists in nature at all. And since it doesn't exist, there is no way one could ever run it backwards, change its rate or travel in it.
All that happens in nature is the progressive occurrence of natural phenomena. Cells divide at the speed which they happen to divide, the granite cliff face crumbles onto the talus pile below as fast as it crumbles, and the earth rotates on and on, independent of any sort of time.
Time is our abstraction. We invented it, just as we came up with the inch and the foot and the mile. We began keeping track of the earth's rotations and invented time based upon a rotation's subdivision, hours at first with sundials, then minutes, once we had managed a reliable clock escapement and eventually nanoseconds. As soon as we had invented these hour and second pieces of a rotation of the earth, we could measure the duration of all sorts of things in terms of them.
And from beginning to end, we remain biological beings. We do not innately look at things from the perspective of a ticking mechanism. Events fly by more as we get older simply because our only natural way of sensing them is by contrasting their duration with how long our life has been so far. A summer for a four year old is a far more noticeable percentage of his life than it is of the life of an eighty year old.
There is indeed a progression of natural events that we are swept along with. And we can call this progression "time" if we must, but our label gives us no mastery at all. We only progress at the rate nature allows. We might someday leap into space faster than light and turn about to see earlier events brought to us by the light we outran, but this is not time travel. We are only fooling ourselves. If we are ever to go rollicking about in the distant past or future, we shall simply have to use magic.