The song is about an aging disc jockey who travels the United States seeking happiness, which he believes he will find by following his passion for being a radio broadcaster, only to discover that his life, looks, and voice have all passed him by, as hinted in the OLD of the title.
After losing his job due to age discrimination (as suggested by the call letters "W-OLD" and "they said that they like the young sound when they let me go"), the singer leaves his family to spend eight years in gigs in Tulsa and then Boise before having the opportunity to again work in his home city.
WOLD-FM is an actual radio station in Marion, Virginia, which went on the air in 1968, five years before Chapin recorded the song.
The live version of the song from the compilation The Gold Medal Collection has an example of this; WOLD was replaced with KHJ, a station in Los Angeles.
[1] However, when Chapin performed it on the Greatest Stories Live album, he jokingly said that the song actually charted for "15 minutes.