There are no hard rules about where a TV should be hung or what the maximized viewing distance is, but here are some general guidelines:
For comfortable viewing height that causes the least eye and neck strain, try to have your eye level be about midway-up the screen. Usually, that measures out at +/- 42″ from the ground if you are seated on a chair or sofa. This height changes to about 60-65″ in a game room where people are watching from a standing position.
To know how far back to sit, a general rule is to take the diagonal measurement of the screen and multiply it by 2.5. This gives you the distance in inches that will be comfortable to most people.