Do you know where the 2nd century Christians came by their information? Wasn’t it through art because they couldn’t read and that is how they passed down stories and information. And couldn’t that have been the artist license to have portrayed Joseph as aged because it was a better protector of Mary’s Virginity; as well as the fact that Joseph is not in the later chapters of the bible, therefore we presume that he was died of old age and there is no real evidence.
As for the virginity… (I can’t remember my source) I believe there was a Saint that Mary appeared to and she had spoken of Joseph being “Just” which in turn took to be a virgin.
I will have to find that Saint and source for you.