Well, young man--yes to me you are a young man :)
You will not become what you do not want to be. The next part of your life there will be people who want to define you, based on their expectations. Don't let them.
Believe me, that spark of joy, of spontaneity, the font of unbounded imagination is yours if you choose to keep it.
When I walk at night with my daughter and her dog I stop sometimes, suddenly, and rejoice at the wonder of the sky.
Those things you treasure in yourself will go, only if you let them go.
The hardest part about the next phase of your life is loss, loss of others mostly. That is the inevitable part of life we look away from as much as possible.