At lot of 4b hair is very fragile, so that it doesn't get to a long length. My mother and my daughter have the same length hair, which is just above bra length, I never had that length, my hair was always medium length, when relaxed just collar length. However when I had a curly perm, my hair grew past my shoulders a few inches above bra strap. My hair is naturally very fine and fragile, however since I started washing my hair or a more regular basis, I rinse my hair at least once or twice a day, I am amazed how fast and how much it has been able to retain length. I always had trouble with my hair, especially the back hair, I suffered from thin ends. Since I have stopped all forms of chemical treatments, except of course of colouring and I take my supplements, my hair is much thicker than it has ever has been, within two years and four months, it's now past shoulder length, stretched out. If someone had told me that my hair would be this long natural, I would have laughed in their face. So I think that although heredity may be a factor, but how you care for your hair, that makes the final difference and I think that Afro texturised hair, especially 4b, needs water, water, water.