Above all, the idea that St. Joseph would be an old man of eighty or more years stands in direct contradiction with the requirements of his vocation. Joseph was to appear publicly as the husband of Mary and the father of Jesus, at least to safeguard the honor of Mother and Son. Yet how could a man of patriarchal years be considered capable of fatherhood? A decrepit, senile guardian of Mary would open the door to public suspicion of adultery and illegitimacy. Again, hard work and trying situations of all sorts beset the Holy Family. How could such an old man perform duties that called for a robust provider and protector?Ignoring the rhetorical excess, the main arguments against the plausibility of an elderly St. Joseph are: (1) nobody would have believed that Joseph was the father of Jesus, (2) he would have been incapable of providing for his family in old age, since he was a manual laborer, and (3) his age would have prevented him from fleeing swiftly to Egypt during Herod's slaughter. In answer to these complaints, let us look at the hardiness of the old, Hebrew patriarchal stock from which Joseph sprang.
- Abraham, progenitor of many nations, was 75 years of age when called by God to the promised land. It was after this that he went to war against the enemies of Sodom and Gomorrah to save his nephew Lot. He was over 99 when he brought his son Isaac up the mountain for sacrifice. He fathered Ishmael and Isaac both in his old age; the only concern about his promised seed was that his wife Sarah was barren, not that he was infertile.
- Job was afflicted when his children were old enough to feast and drink wine on their own, and lived afterwards to see four new generations of his children.
- Moses was 80 years old when called by God to deliver his people from the tyranny of Pharaoh. He led all of Israel through the desert until his death at the age of 120.
- Joshua led the military campaign of Israel into the promised land until he was "old, and far advanced in years."
- Joachim, father of the Virgin Mary, was elderly and long childless when an angel appeared and promised him and his wife a child. In the mean time he busied himself with the tending of his flocks, hardly a lethargic lifestyle.
So, to answer the supposed difficulties: (1) elderly men in the ancient past and in the present day have no enormous difficulty fathering children with younger women, so if God's intention was to hide Jesus as the son of Joseph until his ministry (which is itself contrary to some early speculations), Joseph's age would not be an impediment; (2) being a carpenter or artisan, Joseph probably would have stayed physically fit into old age, and if he was unable to personally work, his sons would have provided for him; and (3) since he was probably fit in his old age, the Flight into Egypt would not have been a great burden.
The matter of the Flight into Egypt is also colored by the traditional iconography that shows St. Joseph on foot while the Virgin rides a donkey and carries the Christ Child. I am not sure that any source earlier than the Gospel of Pseudo-Matthew (A.D. 400-600s) describes Mary riding their only beast into Egypt. It may have been the case that they possessed two beasts of burden, and that Joseph rode one instead of walking. The miracles during the Flight attested by the Coptic tradition would have also alleviated many of the journey's difficulties.