Even if this man weren't twice your age, I'd still strongly urge you to listen to your parents and not pursue this relationship. They love you and don't want to see you hurt -- and they know this is very likely going to happen with this "relationship."
I realize you have a very strong emotional attachment to this person -- and frankly, this makes it hard for you to step back and look at the relationship objectively. But your parents have far more experience than you do, and they know the dangers you face -- not just from the difference in your ages, but because it's impossible for you to know what this man is really like. They probably know too that legal issues could be involved, since you are a minor.
Not only do your parents love you, but God loves you even more, and He knows what's best for you. That's why the most important thing you can do is seek His will for your future. Don't let your emotions lead you down the wrong path.
Ask God for wisdom -- not just about this issue, but also about every decision you'll be making during this crucial time in your life. Begin by turning to Jesus Christ and committing your life to Him. Then put His promise into action: "If any of you lacks wisdom, he should ask God... and it will be given to him" (James 1:5).