For me it was simple. I told them straight-up, that the only reason that we have a relationship, is because I wanted it. I told them that very soon I will be 18, and whether they like it or not, I will attend college, wherever I want. So they can either let me be, and keep a relationship, or try and hold me back, and lose the relationship.
That woke them up to the reality of my age, and they started to soften.
I’m still paying for everything except the deposit myself, but hey, independence.