I don’t agree with the traditional picture of St Joseph as an old man, even though it may have been prompted by a desire to emphasize the perpetual virginity of Mary. I see him as a strong young man, perhaps a few years older than our Lady, but in the prime of his life and work.
You don’t have to wait to be old or lifeless to practice the virtue of chastity. Purity comes from love; and the strength and gaiety of youth are no obstacle for noble love. Joseph had a young heart and a young body when he married Mary, when he learned of the mystery of her divine motherhood, when he lived in her company, respecting the integrity God wished to give the world as one more sign that he had come to share the life of his creatures. Anyone who cannot understand a love like that knows very little of true love and is a complete stranger to the Christian meaning of chastity. (Christ is passing by, 40)