Mary was 17 at the time of her marriage, so that's not unreasonable, but 13 for John seems too young. Although the law allowed marriage from that age, it very rarely happened other than for royalty etc. There are 2 possibilities - that John was actually older than a newborn when he was christened and when he was buried, someone calculated his age from his baptismal record. Or there was another John Challoner, perhaps a cousin, who married Mary and was christened elsewhere and whose burial hasn't been identified yet. In other words, how sure are you that the John that was buried is the same John who was married to Mary?
