Does the Bible say anything about a great difference in age between a man and woman who want to marry or who are married?
There was a ten-year difference in Abraham and Sarah's age. "Then Abraham fell on his face and laughed, and said in his heart, "Shall a child be born to a man who is one hundred years old? And shall Sarah, who is ninety years old" (Genesis 17:17).
David was very old when he married Abishag, a young woman. "Therefore his servants said to him, "Let a young woman, a virgin, be sought for our lord the king, and let her stand before the king, and let her care for him; and let her lie in your bosom, that our lord the king may be warm." So they sought for a lovely young woman throughout all the territory of Israel, and found Abishag the Shunammite, and brought her to the king. The young woman was very lovely; and she cared for the king, and served him; but the king did not know her" (I Kings 1:2-4).
There was an age difference between Ruth and Boaz, though we don't know exactly how much, only that Ruth was seen to be attractive to young men and Boaz was an older man. "Then he said, "Blessed are you of the LORD, my daughter! For you have shown more kindness at the end than at the beginning, in that you did not go after young men, whether poor or rich"" (Ruth 3:10). "There was a relative of Naomi's husband, a man of great wealth, of the family of Elimelech. His name was Boaz" (Ruth 2:1).