Trigger warning : I think i was molested at a young age

Ok this is going to be a little long and im not sure if this is the right section for this. But basically let me start off by saying I am 38 and my brother is 46. When we were very young my mom and dad had a night where they wanted to be alone so they had me and my brothers spend the night at my grandmas house. My grandma had set us up in a spare bedroom. I was about 4 or 5 or so if i remember correctly, my brother was about 12 or 13. In the middle of the night he started asking me if he could put his fingers "up there" and i said no. I was really young but i somehow knew it was wrong and i felt very uncomfortable. I just knew i didnt want to be touched like that. Him begging and trying to convince me went on for at least a half hour. I started to cry and wanted it to stop. Eventually he just went and did it and i dont remember what happened after that exactly but i remember that was it, he left me alone and i went to sleep. Nothing else ever happened like that with him again. As time went on i noticed with us growing up that he wasnt all there. Not super obvious to anyone that didnt live with him but he definitely was a bit off. Its honestly something tho that has always given me bad ptsd. Any time, even to this day i dont like fingers near me, id much prefer to skip that part of foreplay or i have anxiety and growing up i always felt embarrassed and ashamed and felt like i did something wrong. I felt like if i said something people wouldnt believe me and he was my brother who never did anything like that again so i just tried to cover it up in my mind and pretend it didnt happen. I told myself over and over that he was just a curious child. But all these years later in my 30s it has eaten away at me. He was 12 or 13, i somehow feel that is old enough to know better. I just dont know what to think. I dont know if i can label that being molested because of his age or not. I dont know what to say but i know either way it has hurt me so much. I still have to see him every day and as an adult he has actually become a horrible person and we do not get along so i feel like that feeling of needing to protect him i had as child is starting to diminish. Ive never spoke about it to anyone, ever. This is the first time its leaving my mind to another persons eyes or ears, and its scary. But i needed to say it. And i needed to know that im not making a big deal out of something i shouldnt. I was so upset that i started to say something about it to him in front of my mom. I told him he did something to me that traumatized me when i was like 4 and he said i was crazy. My mom later asked me what he did and i told her i didnt want to say. She looked me dead in the eye and said "he did NOT do anything to you" and i got upset. She said "are you trying to say he raped you? Because i wont listen to that because i know its not true" i told her i never said that, i never said anything about it, but the fact that she said that to me and called me a liar without me even speaking about it or saying what he actually did or what it pertained to just hurt so bad. I tried to say something and just couldn't. So im leaving it here. Thank you everyone for listening to my story <3