Well I was reading at this website... www.fanfiction.net/book/twilight (ur own stories about twilight characters) and i was reading a comedy one where emmett get wierd mood swings (thanks to jasper) he cut off rosalies hair and she was yelling at him saying u idiot my hair doesn't grow back so
since carlilse changed edward into a vampire when he was a baby and had very little hair, when and how did it grow and become permanent? i do have some more but i forgot them so i will come back to you
From what I have read and mythology hair continues to grow for a while after you die. So in theory once you are turned your hair would grow for a short time period. Not sure on the length I think it would vary based on nationality, age, location and so forth...
As far as when Edward was changed he was changed by Carlisle at 17, not when he was a baby. If someone was turned into a vampire as a baby then they would stay a baby and thusly not have hair unless they were born with it.