You make it sound like a relationship of choice. It was rape. A rapist doesn't seem like the person that has qualms about age difference.
They had a consensual relationship later.
That's not at odds with him having raped her. In addition, most rapes (and murders, and most violent crimes) are committed by those in close relationships. Double in addition, I don't doubt for a minute that a rapist 40 years her senior would manipulate this woman into a "consensual" relationship post-facto.
A "the worst has already happened, let's move on" approach? That's nasty
To those that will downvote me: I wouldn't prosecute the guy without proof even if I thought he was guilty.