Age difference is too great, and especially developmental difference. You were an elementary student and he was a high schooler/adolescent. A lot of victims of abuse feel shame and guilt for one reason or another, even though they are not at fault. And with this age difference you were not responsible....you probably trusted your older brother to understand the world better. That you objected at some point tells me your body knew it was wrong (though you could also sense it's wrong without objecting because this kind of thing can be so confusing for the younger person). You could even google "normal childhood sex play" or something like that. I'm sorry I can't cite anything but even if your brother was mixed up an didn't mean to hurt you, he likely did because this is "red flag" play....not really play but more like you were taken advantage of...I'd call it sexual abuse but I hope there's someone you can talk to directly maybe to sort through some of the feelings. You might want to minimize but it sounds like it's important...I've had several of these one time events that I thought shouldn't matter but they did...they begged for some sort of processing and resolution.