You are doing common core math.
She is 30. "Teen" can be as young as 13, so 30-13=17. She gave birth at 17 max.
This puts the start at 16 or 17. Not that unusual at all.
I know now-responsible women who had their first child at 14 or 15. Although they don't have neck and face tattoos.
used to be quite common on the farm to marry very young...