So I transitioned from a Little Girl to a Woman underneath my mid teen brother while our parents were out at a wedding.
He and I physically engaged with each other about five times during just a bit over a year. We had one close call with getting caught but our parents never found out how active we were. We are both married & neither of our spouses know anything about our history and I intend to keep it that was. He and I never bring it up but I just know that he remembers it as much as I do. So we got away with it.