Which decisions I make today will affect me for my entire life?

The decision i make today that can affect me for my entire life for example is a job. I am supposed to know what field i want to go into by the time I get out of high school. If i don't know what profession I want to be in then it can affect me in the near future because i would still be living at home with my mother in the basement with no goals or a job. I don't want that to happen so i have to decide what i like to do in life. I love studying the stars for example. So i would like to be a astroonomer when I am fully grown and capable of handling business on my home. I don't want to come out of highschool not knowing what job i want to do or even what college and major i want to be in. It si not in my nature to wait to do things the last minute and jobs and college are the most biggest decision in of my life.