Children sing naturally and spontaneously, sometimes without lyrics or tunes. Youths sing expectantly, anticipating what lies ahead. But the elderly often have trouble singing physically and generally look backward instead of forward. Yet this third song of Christmas has endured 2,000 years; many sing it every Sunday, and some religious bodies have incorporated it into evening prayers every day since at least the fourth century AD. That is quite a claim for a composer of any age, let alone an octogenarian.
We know little of Simeon other than: he lived in Jerusalem at the time of Christ's birth; he was an upright man; the Holy Spirit was upon him; and he was waiting for something to happen (Luke 2:25). T.S. Eliot described him as "one who has 80 years and no tomorrow" in "A Song for Simeon." Since life expectancy was roughly half of what it is today, he was literally living on borrowed time solely because he was waiting for the prophesied comfort or consolation of Israel (Isaiah 40:1-2, 10-11).
Many hold out for fulfillment of some special dream before dying: birth of a child/grandchild, burning of a mortgage, educational/vocational success, etc. One recent study found devoutly religious people often survive holy days before succumbing. Simeon's dream went much farther. He was looking for the greatest possible blessing on his nation, because God promised he would not see death before the Lord's special leader, known in Hebrew as the Messiah and in Greek as the Christ, had come (Luke 2:26).
Although most details remain unknown, I doubt Simeon's expectations were twisted by personal political or military dreams of success. He was not thinking of himself but of his people, who had been without a significant spiritual leader for generations. He must have been a man of great faith, to receive and believe a promise from God that he would not die until his dream was fulfilled, whether he lived with it from his childhood or only after he had become an older man.