It's My Best Sex Memory

We were close growing up, more like brother sister than cousins. We were watching tv after school, I was about to turn 15, she was mid 13. The tickling went into heavy petting, her hard boobs and then rubbing her between the legs. Pulling off her gym shorts and she lay there in panties. And I pulled her panties off, she offered no resistance. I kneeled and undid my belt and pushed my pants down, then my underwear, crawled over her. Letting myself down, I told her to open her legs and in a second I was completely in her vagina.