That's a good question. It is true that adults are usually aware of the consequences of their actions. Perhaps a 7 year old may not have been as aware. It sounds like he was acting out on what happened to him. Perhaps he lost that feeling of control when he was abused and then he probably felt that he could regain that feeling by doing the same to you. However, the truth is, that 7 year old knew what he was doing was wrong. I don't feel you can hold him accountable to the same standards as an adult because he was not one. However, he did use his power over you to hurt you. He wanted control of you and he unexcusably took it. You have EVERY right to be angry about that.
I was abused by an adult and my brother (a child of 13) when I was 7 years of age. My perp was of a different age than yours. I struggled with that one as well. Regardless, my brother was still accountable for his actions and I did confront him years later and made him aware of the damage he caused. If you do decide to confront this individual I would highly recommend getting assistance from a T who could possibly help walk you through the best ways to do so. I wouldn't rush it though.
Truth is the very reason we strive to live. It surrounds and resides within us. Accepting the truths we already know and seeking out those we do not is a direct path to inner balance and joy. For life is not a means to an end, but a journey. Life comes and goes but the truth will always live on.