I'm assuming you quoted me by accident? How do you know they didn't? Historically, the marriage age for girls was rather young, often 12. Now obviously Western societies are dynamic and we've moved on since then while Islam is more traditional and still practices many things that we've moved on from. So it wouldn't surprise me if vikings married girls off at a young age back then like most societies did at the time. A large part of it was that life was short, most children did not survive childhood and childhood didn't really exist as it does now. You were forced to grow up fast and provide for the family one way or another. A major part of a girl's worth was as a bride, while boys worked manual labor and typically got married later when they could better support a wife and children.