I want my life to end on a suicide.

I am doing great in my life, and I am very happy at the moment, i just want to kill myself not now, but when I will feel like dying. I don't want to die being struck by a car in the middle of the street, I want to die when I feel like it, I want to die once I feel like I have accomplished everything I wanted in my life and I'm old enough. I don't want to die to a cancer. I want my life to be in my hands, I want to control my death.