hi everyone. does anybody have an idea how to turn black hair into white? for example aging progess. Thanks.

HMG, welcome to RetouchPRO!
Epending on the image, it could be best to create a mask of the hair so that you could isolate it on a separate layer where you could:
- Desaturate it to turn it gray
- Invert the color
- Use Replace Color command
- Use Selective Color Adjustment
- Make a Hue / Saturation Adjust
- Levels Adjust
- Curve Adjust
......probably anoth half dozen options.

Perhaps if you post the image here you would get more specific advise and detail.
Regards, Murray