The origin of marriage is not Adam and Eve, who were clone self-siblings; the first marriage was of Cain who married someone from the city of Nod. His wife's parents were as old as Garden itself, given they were the same age as his parents... so the fact that she still has grandparents means they had to be older than the universe.
"Salt cures Everything!"
My YouTube: https://www.youtube.com/user/Nirakolov/videos