When T's say "it's up to you" they mean "it's up to you -- you are in control". Sometimes that is not what we want to hear, because we don't feel in control of anything, or we feel that being told we are in control is a lie because we were never allowed to be in control of anything. But I think that is what they are trying to say: now you are an adult and it is in your control, and we are not going to force anything on you. It may not be the best possible thing to say to us when we feel out of control and want someone to be in control, but I think that is what they are saying.