1976, my older sister's freshman year in 1976. (We had no family connection to the school prior to that, so no such tradition).
I remember when she came home on some weekends talking about how good the team was, after she had attended a few games and experienced it.
If memory is reliable, the first game I was able to see on TV (possibly a WOI statewide feed?) was that same season, at Colorado. ISU was ranked that week, I think. It was rare to get television coverage during regular season unless you one of the handful of mega-programs.
I don't recall that much about the game, I do remember Iowa State losing. That's the year CU went to the Orange Bowl and ISU didn't get a bowl bid, I only realized that in retrospect reading The Bomb the next spring.
If that's the game I'm thinking it is, announcers made a point prior to kickoff that it was an unusual start time -- it was 11 a.m. Central, i.e., 10 a.m. Mountain time. Fans who remember that era more clearly can verify/dispute that.