COCSA: Can a victim be older than their perpetrator?

When I was 12/13 and my brother was 9ish, he started to grope me. At first it was just quick grabs of my breasts or ass. But he started to get more confident and began groping and squeezing for longer and longer periods of time and doing it more frequently. Eventually he started grabbing/cupping my vulva through my clothes. I was a bit bigger than him and could successfully fight him off, but I was not allowed to. My parents knew what was happening and he often did stuff like this in front of them. They ignored it and acted like it wasn't happening. He never got in trouble for it. They would only tell him to stop in the moment if there was a guest over or I was begging them to momentarily intervene. But if I pushed him, hit him, or even just yelled at him to stop, I got in trouble with my parents. I cried and begged my parents for months to talk to him and make him stop, but they never did. I was constantly choosing between letting my own brother touch me and getting punished by my parents for self-defense. It was agony. This probably went on for 9 months. I don't know if I'm really a victim of abuse or anything. My brother was younger than me and smaller than me. In COCSA cases, it's almost always an older abuser and a younger victim. That's not my situation. He knew touching me was wrong, but he didn't have a complete understanding of consent and sex. But, he was old enough to understand "no" and me crying. As his older sister, I feel like I also have a responsibility towards him and that I should have done more in that situation. But how could I? My parents didn't help me and I was punished for protecting myself.