I have long hair, and by long I mean it touched my bum. Growing it, well you just have to go for it, I decided one day I would and here I am.
You will have 3 main stages, Emo stage, this will be very very annoying, it will poke you in the eyes, and you will want to cut it, if you fight through this then you will have a couple of months of peace before.
Mouth stage, its now long enough to cover your head, but its going to keep getting in your mouth, and its not yet long enough to tie back. Again you are going to want to cut it.
However after it gets past your mouth, you are going to have long hair, which does not keep poking you in the face. Also if you need to you will be able to tie it back out the way. A warning though, once you hit this stage, if you have facial hair as well, you will become Jesus to everyone you know, more so when drunk.
Then its upto you how long it gets, I will be honest all your friends (And random people in the street when it gets long enough) are going to make fun of you, call you jesus, hobo etc, but if you want long hair just ignore it. Eventualy they will get use to it, and you will get use to being called names, and you will simply have long hair.
I will also add (In before gay) that long hair is a fair bit of work, you will need to wash it and condition it at least every couple of days, and combing it in a morning is a royal pain, but well worth it. Because if you ignore looking after your hair, you are going to look like that guy who never takes a shower, and has lard in his hair... Which is not cool!
Jcb33.