My brother molested my younger sister with autism when he was 13 & she was 10. Depending on your state, there is no statute of limitation on a crime committed involving a child victim. I work with juvenile sex offenders; in MN, you can be charged as a sex offender as a minor. A two year age difference between the offender & victim is all it takes. Legally, my brother should be a sex offender. He did this twice (that we know of) & never paid for what he did. My mom stood up for him, saying "it's natural to be curious." My dad almost divorced her over this & still to this day (20 years later), he hasn't forgiven my brother. He never apologized & I don't think he ever will.
I understand you were a child, but I really hope you understand what you did. I don't blame your sister one bit; I couldn't imagine carrying that trauma & guilt/shame/ sadness those many years. I'm sure she felt so alone for so long. I'm glad she found it in her heart to forgive you - pretty bold, considering.