I can give you a parent's perspective from personal experience. I had a teenage son who wants to join the Marines.
As a parent, I want my son to have options. I tell him this. I want him to get good grades and to be safe. These are things that will help him whether or not he ends up in the military.
When I see my son being responsible and working on his classes and other activities, it helps me to take him seriously... it is a matter of maturity. When my son started getting his butt out of bed early in the morning and on weekends (on his own initiative) to do exercises with JROTC, I really started taking him seriously.
You should also try to see things from your parents' point of view. Having a child in the military is a scary prospect. We all worry about our kids and none of us want to see our kids in harms way. Of course, as a parent I will support my kids no matter what they decide to do... and of course I will be proud of my son if he ends up in the military. As engineer pointed out, you have a few years to think about it.
If you work hard at school and learn responsibility. You will do well and gain the respect of your parents whether or not you end up in the military.