Sillychinchilly,
Unfortunately, I have some experience in this area...not from something that happened to me, but something that was done to my foster daughter.
The first thing you would need to do would be to contact the state's attorney. There may be a statute of limitations on the crime committed, which would mean he could not be charged for what he did. The state's attorney could also discuss with you what evidence you have and whether it would be a case he/she could have a chance of successfully prosecuting.
It will be hard for you to hear, but you have to know that after so much time has passed, it is likely the attorney will tell you it is a case he could not prosecute. Many cases of this nature end up being unsuccessful because of lack of evidence. Did you see a doctor or a counselor after this happened? If you did, in most states medical doctors, school counselors, social workers, teachers, and psychologists are all designated mandated reporters. This means, by law, they are required to report any knowledge they have of abuse or illegal activity involving a minor.
If you spoke with any of those people after the crime occurred they would have been legally required to file a report with child protective services. So there could be a report on record, which would help support any testimony you gave in court.
I would ask you to think about what you want to do, though. I would not by any means discourage you from pursuing this if that's what you feel you need to do. But cases like this can be VERY difficult on the victim emotionally. Do you feel able to handle telling your story in open court, in front of family, friends, and most of all in front of your abuser? I have worked with a victims' advocacy group that handles many cases like yours, and many of the victims find it very hard to face their abuser. Most feel empowered once they have done it, but the experience can be very hard emotionally. Again, I don't want you to think I am discouraging you. It is very brave to have come forward like you have already. And there is at least one more option available to you, if you cannot go to court.
You can file a report with your local child protective services officer about what happened to you. Particularly, if you have any knowledge that this man has contact with children or teenagers currently, I would encourage you to do this. CPS is required to investigate all allegations involving the abuse of children. At least it would let him know that he is being watched to a certain extent, and may cause him to be more hesitant to hurt another child like he hurt you.
The most important thing in all of this, though, is that you do what you need to do to heal emotionally. This kind of experience is one that never goes away, but there are ways for you to come to terms with what happened and to learn how to move past it, to not let his actions control your life or your feelings anymore. I would urge you to join a support group for survivors of sexual abuse, if you have not done so already. I know many people have misgivings about support groups and feel awkward about the idea. But they can be tremendously helpful in these situations. Victims of sexual abuse almost always carry tremendous feelings of guilt and shame, they often feel responsible for what was done to them, and mostly they feel very, VERY alone. In your posting you said "now that they (your grandparents) can't stop you", so I assume they are not in support of your decision. I would urge you to find a counselor who specializes in dealing with sexual abuse victims, and their families. Family support is vital for a victim of abuse. They need to understand that you have to find a way to empower yourself, so that you can move past this to a healthier life. That is something they need to support, no matter what.
I am so grateful you had the courage to post this, and not remain silent, as it seems you have been forced to do until now. It took tremendous strength for you to do that, I'm sure. I hope what I have said is helpful. I would like to end by saying that no matter what happens, in court, with your family, or anywhere else, you need to do whatever it takes to feel like you can be ok. The most important thing is for you to find a way to move past this, and not let your abuser have power over you anymore, to not let this control you or your life choices, and to
never, EVER blame yourself for what happened.
