What happens next?

How to convince your parents to let you grow your hair (boys )
Prove that you are deserving.
When you're able to prove to your parents that you are a mature, responsible and upstanding young man, they will be more likely to give you more leeway. Try not to break any rules and try to take on more responsibilities; this will allow your parents to see you in a different light.
Figure out small tasks that your parents would see as acting with responsibility. For example, add a chore like washing the dishes, or cleaning your room without having to be told to.