Tom Selleck in "Blue Bloods."

If you are old enough, you may recall that back in the television season of 1973-74 the first two hours of CBS’s Saturday night line-up were filled with, in this order, “All in the Family,” “M*A*S*H,” “The Mary Tyler Moore Show” and “The Bob Newhart Show.”

And, according to that season’s Nielsen ratings, all were in the top dozen of the year’s most-watched programs. At No. 1 was “All in the Family.” Close behind, at No. 4, was “M*A*S*H.” “The Mary Tyler Moore Show” was ninth and “The Bob Newhart Show” was 12th.

Back in the day, and I mean way back in the day, which is to say wayyy back in the day, Saturday night boasted line-ups that were not just pretty good but were “appointment TV,” shows you looked forward to all week. And at the time this was serious competition for movies, sporting events, concerts and your daughter’s dance recital.

These were among the most popular TV shows of the era and there was no time shifting, no streaming, no way to see them again until summer reruns, which were months away. If you wanted to be in on Monday’s water-cooler TV discussions, these sitcoms were high priorities.

One of the highest-rated shows of all time, “Gunsmoke,” was also a Saturday night staple for its first 12 years, as was “Bonanza” for its first two years. And among other popular, memorable Saturday night shows were “Perry Mason,” “Route 66,” “The Outer Limits,” “Get Smart,” “WKRP in Cincinnati,” “Mission: Impossible” “Leave it To Beaver,” “My Three Sons,” “I Dream of Jeannie,” “Hogan’s Heroes” and “Emergency!”

Another thing all of these shows from the 1950s, ’60s and ’70s have in common is that they are currently being shown on the MeTV channel and the Antenna TV channel, both of which specialize in programs that were once syndicated rerun staples but are now considered little more than baby-boomer nostalgia.

Personally, I think of them as classics.

So what happened to Saturday nights? Why are Saturdays now the boneyard of the television landscape? Have you noticed that the major networks are showing reruns that night, and many of them are episodes that debuted just a few days before?

Well, here’s the answer. TV execs have determined (by crystal ball, I’m guessing) that no one in the coveted 18-49 demographic watches TV on Saturday. That’s right. Apparently it’s only old fogies like me; the over 50s. (OK, the over 60s, too.) And as everyone knows, we don’t matter in the Nielsen ratings, those tallies that determine how much networks can charge for commercials.

Similarly, Friday nights are also considered a sort of young peoples no man’s land, where the networks put programs in which they have no faith. The family cop show “Blue Bloods,” which stars Tom Selleck, for example, is a show that consistently draws high numbers, but they aren’t the right kind.

According to websites that keep score, “Blue Bloods” often attracts twice as many viewers as the other shows competing in the same time slot, but the Nielsen ratings, which reflect the 18-49 demo, are lower because most of those viewers are too old.

A recent news story about the show suggests that “Blue Bloods” is constantly “on the bubble,” which is TV-speak for “being considered for cancellation.” As it happens, the show has been picked up for a fourth season, which will carry it through May 2014, but the threat hangs over the series like a constant cloud as the bosses keep asking what they can do to get younger audiences to watch.

Which is a conundrum that approaches the very definition of “Catch-22”: “Blue Bloods” is placed on the Friday schedule because the network doesn’t believe anyone watches TV on Fridays. But, hey, someone must be watching because the show is garnering large audience numbers. Sadly, those numbers are the wrong age group. So let’s change the show to draw in younger viewers — you know, the kids who don’t watch TV on Fridays. Of course that might alienate the older audience that is watching but they don’t count anyway. And if the numbers drop we can cancel the show and try a new program that might draw a younger audience. Not that we’ll put a good show in that slot since no one watches TV on Fridays.

Say what?

And, really, why does it even matter anymore? Thanks to various recording devices and streaming sites, no one watches TV shows when they are first shown anyway.

Nonetheless, quite a few programs have been canceled over the past several years, even when their ratings numbers weren’t bad, simply because it was determined that those numbers were generated by people over 50. I know I’ve written about this before but, really, do they think people over 50 don’t buy things?

Comment on this story

I bought a new car a couple of years ago when I was 62 and no one at the dealership balked at taking my money, even though I had crossed the dreaded 50-year-old dead-in-the-water demographic some 12 years earlier. Ditto the TV we bought a couple years back, the computer we paid for at a major outlet, the new cellphone my wife got a few months ago, the food and household items we buy every week or the various purchases we make online.

Many of which are items we saw advertised while watching “Blue Bloods.”