I wanted to be a surgeon my entire life up until around the age of 15. At 15 I decided I wanted to go to space and become an astronaut. I gave it my all and even set out a life plan to accomplish this:

1. Study physics in college. Age 18-22
2. Go to medical school and become a surgeon. Age 22-34
3. Have the Air Force pay for my medical school.
4. Spend time in the Air Force, since I'd have to if they're going to pay for my schooling, but get my pilots license in the meantime. Age 34-44. Most likely required ten years of service, but maybe only 34-39. I'd also be an officer with a medical degree.
5. Join NASA. I'd be a surgeon with a physics degree and pilot's license, as well as retired military. Seems like an appropriate resume to become an astronaut.

However, as I was on the path towards medical school, even though I was a physics major, I was required to take other necessary classes such as chemistry and organic chemistry. So, my third year in college I changed my major to chemistry because I had fallen in love with it.

Do I regret not sticking with my original plan from over half my life ago? Not at all. I've been working as a chemist for a decade now and I still love it. However, to be honest, my dream now is to one day open a restaurant/bar (maybe even multiple).

So, the point of my story is that you'll change as a person as you age, and your dreams and passions will also change in the process. But, that doesn't mean you shouldn't do everything it takes to accomplish that dream. You'll grow by venturing out, learning new skills, trying new things, and it's even possible (and highly likely) that you might discover another dream or goal along the way that you find much more exciting.