How old was Joseph when he married Mary?

I can only guess.

Joseph was a G435-man, Luke 1:

27 to a virgin pledged to be married to a man [G435] named Joseph

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Matthew 14:

21 The number of those who ate was about five thousand men [G435], besides women and children.

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1 Corinthians 13:

11 When I was a child, I talked like a child, I thought like a child, I reasoned like a child. When I became a man [G435], I put the ways of childhood behind me.

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Is there anything we can infer about Joseph's age from the use of 'man' to describe him in Luke?

Not much other than that he was supposed to be a mature, responsible man who ate more than a child.

On the other hand, we know that Mary didn't marry Joseph for his money, Luke 2:

22 When the time came for the purification rites required by the Law of Moses, Joseph and Mary took him [baby Jesus] to Jerusalem to present him to the Lord 23(as it is written in the Law of the Lord, “Every firstborn male is to be consecrated to the Lord”), 24and to offer a sacrifice in keeping with what is said in the Law of the Lord: “a pair of doves or two young pigeons.”

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I don't think Mary married some rich old man. They were too poor to afford a lamb, Leviticus 12:

7b “ ‘These are the regulations for the woman who gives birth to a boy or a girl. 8 But if she cannot afford a lamb, she is to bring two doves or two young pigeons, one for a burnt offering and the other for a sin offering. In this way the priest will make atonement for her, and she will be clean.’ ”

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Later in Luke 2:

42 When he [Jesus] was twelve years old, they went up to the festival, according to the custom. ... 48 When his parents saw him, they were astonished. His mother said to him, “Son, why have you treated us like this? Your father and I have been anxiously searching for you.”

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When Jesus was 12, Joseph was still alive.

Joseph was a laborer, a carpenter, Matthew 13:

55a “Isn’t this the carpenter’s son?

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By the time of Jesus' public ministry at 30 years old, there was no mention of Joseph being alive.

I am a romantic I guess Joseph was a physically capable man of moderate means in his 20s when he married.