Never think that age will ever be an excuse. Never think that because you are young, you are allowed to mess once or twice. Never knowingly make a mistake unless its furthers a more important idea.
Plan your life from now, think of ten years, see where you want to go, capture those moments in your dreams that make you think of yourself as the best thing that could ever have happened to this world. Be broad and flexible enough to adapt to changing circumstances. Most of all, keep your best thoughts to yourself, they are your jewels which will play their rightful role at the right time of this life.