How many years do you think it will take till humanity develops time travel?

I don't think it ever will be invented, or once it is, they'll destroy all of the research and data on it because it would be too dangerous to travel through the time streams.

I highly highly highly doubt it will ever exist. To control time, you'd have to stop time. To stop time, you'd have to stop every.Single.Atom. in the universe.
And besides, picture this:
Say the government allowed one person to go back in time.
Lets say I went back in time and somehow prevented my sister from getting a brain tumor (she really has one, by the way). Then time would continue, and all the things that have happened because of my sister getting a brain tumor, would never have happened, because if they were caused by her getting one, and she never got one, it never happened.
And so, as time goes by, the me from the past gets to go back in time, and I do something else.
Since I did something else, my sister would then have gotten a brain tumor, and that would continue for all eternity.

TL;DR: It can't happen, and even if it could, it'd cause insane confusion.

To travel time, one would have to experience it as if it were a concrete thing. That would mean that everything that everyone does is a predetermined thing. No altering would be able to occur unless that was the fate of the person to do so.

If all of this is true, then wouldn't that be disheartening to learn. Everything you do has already been decided. You do not make choices, you simply follow the path in front of you. Furthermore, in the event that someone were to attempt to alter time, they would in a sense be attempting to alter fate, and they would probably cause everything to stop existing in doing so.

We won't.

Time isn't linear so you can't just jump back and forth on it.