I want to be an actor because it has been my dream since childhood.
When I was a child my sister and I staged performances every summer.
This is the only thing that I want to do in my life.
I truly feel that I was born for it.
It is my passion, my aim, I (do) devote my life to it and living it.
really good, you don't need the "do" but if you leave it in it emphasizes the "devote"