Green Card Question! (age question)

[Lollipops]

I am currently the daughter of a J-1 visa holder (I think that makes me a J-2). My father is currently in a postdoctoral position meaning it will be a while until he is eligible for a green card. So my question is regarding age requirements. Once my dad has applied and gotten his green card I will probably be older than 18 but younger than 21. I really need that green card ASAP to get scholarships and to get into colleges. So my question is, Am I still dependent on him while I am younger than 21 years of age?
Thanks.