cannot change Cube Speed Over Time

Simply Iam instantiating cube and giving them translation at a specific direction based on a speed variable , when i want to increase the speed over time in type in the update CubeSpeed += 1*Time.deltaTime; That Suppose to increase the Speed by 1 every 1 Second but it doesn't .. the old Cubes that are instantiated are having the old Speed and the new instantiated one are even though i reduced the num to a very low number like .0001 and it still extremely fast , i tried a function and Invoke Repeat it but it doesn't work and a very strange attitude happened when i removed it again , the cubes are instantiated normally in the beginnig and then the cubes get closer and closer although i didn't change the time at all ,i also tried to make it change based on the time passed so i used the function that are commented below but it didn't work either !!! + my game is endless so how am i suppose to make it endless so how am i suppose to increase it without using invokeRepeating or even the Update? i just want to speed the cube over time why the hell it doesn't work ?? here is the very simple code i used

static var CubeSpeed:float =.5;

private var TimeNow = Time.time;

//private var CurrentSpeed=2;

private var PrevTime=0;

// // // function Update () {

transform.Translate(0,0,-.1*CubeSpeed);

     if(transform.position.y >=10.13507)
 
 {
     Destroy(gameObject);
 
     GameController.Score +=10;
     
 }

// if(TimeNow - PrevTime >=3)

// { // //ChangeCubeSpeed (1);

// PrevTime=TimeNow;

// } // Debug.Log(CubeSpeed); //// // function ChangeCubeSpeed( n:float ) //{ // n= .5; // CubeSpeed+= n; //} // //
//
}