When Montag first shows up at Faber's house, at first Faber is reluctant to reveal any information about himself or his previous life. But when Montag reveals himself to be trustworthy and seeking answers, they start making plans. In talking, Faber mentions a few things about his previous life; he was a professor, and in talking about it, says,
"I know a man who printed our college paper half a century ago. That was the year I came to class at the start of the new semester and found only one student to sign up for Drama."
So, according to that quote, we can guess that half a century ago, which is 50 years, papers were still being printed, even though they were on the steady decline in popularity. Faber mentions that not soon after that newspapers pretty much disappeared completely because people weren't interested in reading them anymore. That is a pretty quick decline; it only took a few decades for their society to degenerate into an entertainment only place where people chose to be amused rather than educated. I hope that helped; good luck!