Opposite of Nick, I'm probably in the "older than" category for APS. I'm trying to remember far enough back, and for 40 years ago, I'm not sure if I'm recalling correctly.
But for 1980, I don't think I really recognized any media bias. Remember at this time it was "the big three" TV news services and newspapers, so it would be harder to compare and contrast since IIRC, they didn't vary all that much in their reporting.
For 1990, I don't think I was recognizing media bias, but I might have been questioning some things.
For 2000, I know I was questioning things, and part of that was my exposure to university and grad school in the 90s. Not that the university professors swayed me the way they wanted to. The more they talked, the more I questioned, and not just them, but what I saw and read in the news. It's when I think I first saw blatant bias being pushed.
By 2010, I fully knew there was media bias, and much of that was, and has been, because of alternative news sources via the interwebz. If it wasn't for these, basically investigative journalists posting on bulletin boards, starting web pages, then getting to where they are today with full blown news sites, I would have missed the majority of MSM bias. Having all these "upstart" people dig into stories and provide documented evidence really affected the way I looked at the MSM. The MSM attacking them helped cement my view of media bias.
Now in the last four years, I have seen more than in the previous 36. Especially with what the tech giants have done regarding censorship and altering the news. That has opened up a whole new area of bias, and it scares me much more than MSM bias. At least with MSM bias, I can read alternate views from other sources and make up my mind. But guess what? That's only as long as the tech giants let me see those alternate views. The way they have been censoring and editing - not just news, but as I griped about earlier last month even things like Netflix editing fictional shows, I'm not given the range of information that I would need to make up my mind. Big tech is making up my mind for me by providing only the views they allow me to see.