Right. They never say, "Come on in. We want to get you to confess so that we can arrest you." And they don't have to tell you what they really want. You could have said no, and you didn't. If you knew that you weren't really free to leave, then he should have given you Miranda warnings. Again, however, you'll be able to challenge this when the case comes to court.
Because you were a juvenile at the time of this alleged incident, juvenile court has jurisdiction. The DA will petition to move it to adult court. Your first court date will be your arraignment, where the charges are read into the court record and you are asked how you plead. You must tell the judge you plead not guilty and you can then ask the judge for a free lawyer. He will adjourn the case so that you can come back and meet your lawyer.
From there, you will have two broad choices. One would be to take a plea offer from the prosecutor and the other would be to fight the case, all the way to trial if necessary. Your lawyer will be able to see discovery material, such as the police reports, and he will go over the strengths and weaknsses of the case, and you'll decide how you want to go forward.
Even though the charges are serious, they happened a long time ago, and the police never placed you into custody. So as long as you make your court appearances, you should be able to fight the case while at liberty.