With regards to reporting to the police, yeah that is the 'correct' thing to do, but after 13 years they cant really convict him of anything. Yes it may protect him from doing it to others, but I fear it may important to protect number one at the moment.
If you would (and I hate to use an american-ism) obtain closure by reporting to the police then yes, do it immediately.
I personally doubt if being dragged through it again in a very detailed, potentially very traumatic way, will be helpful to you while you are obviously hurting so much. The other side is that your parents would be forced to face it again, as would your auntie, which could make it very difficult in the short term.
I think the first thing it is important to do is get yourself some counselling. Talk to someone about it, who is unrelated, who is not trying to protect anyone, and who just wants to help you get over it. Tell them everything, and give yourself chance to move on. You may find that in time you feel ready to speak to the police, and will be in a strong enough position to do so.
You are very brave to be thinking about facing it. Telling your friend was a very big, and very important step. Admitting that was part of your life is vital, and the first stage of moving on...the next step is to try and put it where it belongs, in the past. If this involves talking to the police, then do so. If this involves seeing a counsellor, do so. Do whatever is right for you at this moment, as you have been carrying around this heavy burden for a long time.
I know I have given a very different view to the majority of people will, I have my reasons.
I hope it all works out for you.