This song was written and sung by Stephen Stills. It tells the sad story of a man who is born into a poor family and finds himself alone in his old age, wishing for death to come. In the CSN boxed set, Stills explained: "It's about an 84-year-old poverty stricken man who started and finished with nothing."
Running 2:10, the only instrumentation on this track is Stills' acoustic guitar. He recorded the song in one take and planned to use it on his upcoming debut solo album, but when his bandmates heard it, they implored him to use it on the CSN&Y Déjà Vu album. He recorded the track in one take and planned to have David Crosby and Graham Nash sing harmony parts, but they refused. "They told me they wouldn't touch it," said Stills. "So it always stood alone."
The man in this song is 84 years old, but Stills sings that he was born "Four and twenty years ago." Logically, this would mean that he's 24 years old, but there is a bit of poetic license here, as "Sixty-four and twenty years ago" doesn't fit the meter. "Four and Twenty" is a phrase popularized in the children's song "Sing a Song of Sixpence," where four-and-twenty blackbirds are baked in a pie (one of the more disturbing kids' songs).
"4:20" is also associated with marijuana, but that doesn't apply here. Another close cousin is "four score and seven years ago," the first line of Abraham Lincoln's Gettysburg Address.