As recently as the great depression, large age differences were acceptable and common for economic reasons, not because people were more open minded. Older men (20s) commonly married young girls (preteens-teens) because farming families had too many children, and needed to marry daughters off to someone who could support the child, since a daughter is not only a mouth to feed, but not as much help as a boy in working their land. For example, sociologists often reference a 22 year old man who married a 9 year old girl in the smoky mountains in the 1930s. He gave her a doll for a wedding present. Some people have cited instances in history when the family of a young bride such as this one made an agreement with the older husband that the marriage would not be consumnated until the girl was older. It was a matter of money, and connections, and social networking.
Today, however, with industrialized nations, small families, and no land to work or farms to maintain, it is simply no longer economically necessary or acceptable to marry young people off to older people, and certainly not to be having sex with them. The boy was a child. She was not giving him experience, she was abusing him. eVen if he wanted it or something, she should have known beter, because he cannot make that decision for him.