I don't believe him.
There is no way a 13 year old can pass as a 19 year old. The other way around is much more likely. This is either a person who chose not to see the reality or he is plain out lying. If the girl was 16 I'd be more inclined to believe him.
In any case, I think he should stand trial. The judge should take into consideration that he approached the father and told him about the events, although that doesn't mean his motives were pure.