If a person dreams a lot since young, does it mean that he/she is a very imaginative person? Or vise versa?

No, dreaming has nothing to do with being imaginative or not. All of us dream everytime we sleep. It occurs in the stage of Rapid Eye Movement (REM), during the last stage of our sleep. It's just that sometimes, our brain transfers the dream into our unconscious, that's why when we awake, we don't remember the details or we don't even remember that we dreamed at all. It is one way of our body to protect us from all unnecessary or hurtful thoughts. If this things leak into our conscious, we might suffer or die.