Since 1947. (72 years)?
Back then, college FB was bigger than the pros and, during the WW2 years, the military academies were big so I started out an Army (Blanchard, Davis and Arnold Gallifa) fan.
The first afternoon college football radiocasts came on right after a kids' show called "Let's Pretend" (directed/produced by Sybil Trent and Nila Mack.) First game I listened to was the Ohio State Buckeyes vs. the Iowa St. Hawkeyes.
I was a StL (baseball) fan before I rooted for the Chicago (football) Cardinals - Standard question each evening when my father returned from work: "Did the Cardinals win today?" Favorite StL Cardinal player was CF Terry Moore.
Caught up with the football Cards during their 1947, '48 championship seasons. TV had just been invented and I got to watch the Cards lose the "snow game" vs. the Eagles on our b & w TV. (Cards featured their "dream backfield" of Trippi, Angsmann, Harder and Christman. Eagle stars were Steve Van Buren, Pete Retzlaff and (I think) Pete Pihos).
Note - Single Wing football was mainly a college deal - only pro team running it was the Steelers, featuring Joe Geri. Since my uncle Edgar and older brother Jim were Yale attendees, I rooted for the Bulldogs from New Haven (QB'd by Levi Jackson) for most of the 1950's.
Pro football was kind of like college football's poor little brother, but the
NYC metro area was blessed with The NY Football Giants, the NY Yankees (Buddy Young, Spec Sanders and Arnie Weinmeinster) and the Brooklyn Dodgers (Sonny Grandelius and Bob Chappius.
Biggest upset I remember was when John Swiacki's late-game finger-tip catch of a deep pass from Lou Kusserow allowed the Columbia University Lions to beat the favored Army..
That's all I got.