The fastest I have ever seen was in the early 90's. I met this lady in a club and danced with her. her hair completely covered her face when she danced and it was just shoulder length. I seen her from time-to time in different places. Her hair grew to below the butt after several months of not seeing her and this was just several months. The next time I seen her which was about 6 months later was about 6" below her knees and the next time I seen her was about 1 year later and it was just to the bottom of her feet. That is about 3 years growth. I haven't seen her since. She did tell me that her hair grew like a weed. and when we first met that it was past her ankles and she had just cut it that week. DARN IT. Wish I would have met her then.