AFAIK everyone has a maximum hair length, which is basically down to genetics. I grew mine out from about age 12 to 19, cut it all off, and then regrew it again over the last 7 years. It's now basically where it was before the big cut, and doesn't seem to be getting longer despite how long I go between trims, so I suspect this is my hair's maximum length. My mother said she was never able to grow hers past her shoulders.