“Old Days” is a song written by James Pankow for the group Chicago and recorded for their album Chicago VIII (1975), with lead vocals by Peter Cetera. The second single released from that album, it reached #5 on the U.S. Billboard Hot 100 and #3 on the Easy Listening chart.
Pankow has said that the song is a nostalgic piece about his childhood:
“It touches on key phrases that, although they date me, are pretty right-on in terms of images of my childhood. ‘The Howdy Doody Show’ on television and collecting baseball cards and comic books.” 
Cetera apparently hated singing the song in concert, as the Howdy Doody show was his least favorite show during his childhood.
The song is still popular at Chicago concerts, with Jason Scheff or Keith Howland now singing the lead vocal. The Sopranos star Vincent Curatola has been known to guest vocal with the band on the song as well.
“Old Days” is featured on the soundtrack of the movie Starsky & Hutch (2004). The band also reworked the song in 2009 to serve as the theme for the “Monsters in the Morning” show airing on Comcast SportsNet Chicago.