Calculation trouble on mobile

Calculation trouble on mobile

Good morning,
I need to make a calculation ( age^ -0,13)  
To perform this I do:
  1. var age = 22 ;   /* Here simplified, in reality the result of date calculation */
  2. var K4HF = Math.pow(age, -0.13);
  3. var K4HFB = parseFloat(K4HF);

  5. var test = typeof K4HFB;
  6. alert(test);
  7. alert(K4HFB);
  8. alert (K4HFB.toFixed(2)) 
This works fine on Safari Desktop
The first alert give me : number
The second the value : 0.6690907894046102
And the last one the value : 0.67

Exactly what i need

But the result on mobile give:
Fist alert : number
second : NaN
third : NaN

Could someone tell me what I'm doing wrong ?
Thanks