Welcome to our site. I hope you find it to be a place of support and healing.
I'm not sure what the law is in the state where you were abused 20 years ago, but in most of the United States, the statute of limitations are so minimal on sexual abuse of children that you will probably not be able to file any criminal charges. You should check it out however. The information should be readily available on the internet or even the public library. If you go to a public library you may even be able to get a librarian to help you find what you're looking for.
If the statute of limitations has expired you may still be able to file civil charges against the person who abused you. One up side to filing civil charges is that the evidence to convict the person doesn't have to be quite as solid as it does for criminal charges, but it will probably still be an uphill battle for you.
The most important thing to do is consult an attorney about what you are considering. If you are filing civil charges he may even decide to take your case on a contingency which means he is speculating that he can win and will take his fee from the proceeds of the judgment. This also means if you loose you will not have pay the lawyer fees.
Above all, make sure you are prepared for the emotional trauma that will result from the trial resulting from the charges you file. It will do you no good to go through the trouble of filing the charges if you find that all the muck the opposing lawyers dig up about you gets you in such a state that you have a nervous breakdown in the middle of the trial. If you decide to go through with it, make sure you are seeing a therapist regularly.
I've listed a bunch of general information for you to consider. Some of the other men may have more specific information for you.
"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting 'Holy Shit! What a ride!'" ~Hunter S. Thompson