How long has television existed in Ray Bradbury's Fahrenheit 451?

According to Kingsley Amis in New Maps of Hell: A Survey of Science Fiction, Bradbury projected his novel forty or fifty years into the future. Since he published the novel in 1953, when televisions had only been in American homes since 1945, he was imagining television in the late 1990s. At this point, it would have been around for about fifty years in his dystopic world. This would mean more than two generations had been subjected to television, if a generation is assumed to be twenty years. Most people alive in Bradbury's new world would not remember a time without television.
Beatty, a repository of knowledge, believes television rose up as people began to willingly abandon books and reading and that this new technology helped fill in a gap in people's lives.