Hey Mindymouse,
From what my understanding is of the hair growth cycle, once you reach the maximum life of your hair, it goes into the telogen phase, the last phase of the 3 growth cycles, and then the hair sheds itself, making way for a new hair to grow.
In that case, we all have a maximum length our hair we can reach. But at 6" of growth a year, (which is said to be the average for everyone, with some experiencing even faster growth, and a few experiencing a little less), and assuming that most of us have at least a hair growth cycle of 3 years, I believe that we all have the potential to have at least, 15"-18" of hair on our heads; we really do.
The trick is keeping the growth we get. I do believe, that if AA women didn't have such naturally dry hair that breaks a lot at the ends, we would have longer hair on our heads. If we can't keep the ends of our hair on our heads, then we won't experience length, and that's where the challenge is; seeing the growth we really do get by keeping the ends of our hair from snapping or breaking off. /images/graemlins/smile.gif