I'm almost 20. Why do I still have acne?

I was told that when I’m older, my acne would clear and be gone. Why do I still have it? Do I need to eat differently? Is there something wrong with me? Are any of you in the same position as me or have you ever been? If you currently have acne, how old are you? If you used to have acne, how long did it take for it to clear up? What is the best way to get rid of it? In other words, what actually does work?