One additional question, just to add a possible twist to the story: Is it possible that this man believes your daughter is older than she is? I have know plenty of girls who find great pleasure in knowing an older guy is interested in them and they are not always forthcoming with their correct age.
It could be he knows full well, in which case there is no doubt it is a concern, but it could also be that he thinks he is dating someone older, especially since he obviously hasn't been brought around to meet the family all this time.