I'm pretty clear that this song is about not losing your childhood dreams (the part about "and they used to say that someday you'll forget it, you won't hear them": Not hearing things you used to is growing up and losing your dreams), and taking the opportunity (apparently once missed) to go and realize those dreams. In SP's case, it is probably about having a musical career rather than a humdrum existence, against the wishes of parents and other authority figures.
I'm pretty clear that this song is about not losing your childhood dreams (the part about "and they used to say that someday you'll forget it, you won't hear them": Not hearing things you used to is growing up and losing your dreams), and taking the opportunity (apparently once missed) to go and realize those dreams. In SP's case, it is probably about having a musical career rather than a humdrum existence, against the wishes of parents and other authority figures.