Just a couple of thoughts. The tradition that that Joseph was considerably older or even an old man grew out of the desire to emphasize the perpetual virginity of the Blessed Virgin Mary which is a dogma of the Church. St Josemaria de Escriva thinks Joseph was a young man, perhaps a few years older than Mary when they married. Joseph and Mary had a true marriage and it would not have been normal for Mary to marry or to be betrothed to an old man. Further, Joseph took Mary to Bethlehem for the census where Jesus was born and then they took flight to Egypt upon the Angel’s message to Joseph. Then from Egypt, the angel told Joseph to go back to the Holy Land where they set up home in Nazareth. Now, all these journeys would not be suitable for an old man but rather for a young man who had the strength and vigor for such journeys. Joseph is also the Patron of the Universal Church and the greatest saint next to our Blessed Lady. Joseph was called by God to be the foster father of Jesus and the husband of Mary and to provide the support for the Holy Family. Jesus learned the trade of carpentry from Joseph. Joseph was also a very pure and chaste man being the husband of the most pure Virgin Mary and the foster father of purity itself Jesus, the Son of God. From all these considerations, Joseph was most likely a very pure, chaste, virtuous (Holy Scripture calls him simply, a just man) young man when he married our Blessed Lady. The “brothers” of the Lord mentioned in the scriptures are relatives or cousins of his, that is, relatives of Joseph or Mary. If we consider that Joseph was most likely a young man when he married Mary, then these relatives of Jesus are definitely not sons or daughters of Joseph from a previous marriage and they certainly are not the offspring of the Blessed Ever Virgin Mary.