The Tuesday ratings are in, and CBS just delivered another boffo night in terms of total viewers, as my colleague Rick Kissell reports.

As for the part of the audience generally sought by many advertisers, though, here’s a cold splash of reality: More than two-thirds of those viewers don’t matter.

Sifting through Nielsen data from the night shows that overtwo-thirds of the audience for CBS’ “NCIS,” its “L.A.” spinoff and the new drama “Unforgettable” registers in the 50-plus age bracket. And as we all know, none of those folks drink beer, drive cars or buy groceries, so who gives a shit about them?

So much for the 10 million people 50 and over who watched “Unforgettable” (which drew 14.1 million viewers overall), or the estimated 13.5 million of “NCIS'” 20 million viewers born before John F. Kennedy’s inauguration.

On the flip side, advertisers are understandably gaga about Fox’s “New Girl,” in part because 60% of its 10.3 million viewers fell into the 18-49 demographic sweet spot.

We take this preoccupation with youth for granted on a daily basis, so it’s nice to occasionally pause and point out the chasm between TV as a commercial medium and as a cultural barometer.

No wonder CBS research guru David Poltrack keeps trying to find novel ways to change the conversation about ratings and demographics. It’s not that CBS isn’t doing fine by any way you choose to slice the data, but why willingly throw away that much of the chicken?

Still, let’s give all those AARP-eligible “Unforgettable” viewers a hand. Not only did they remember to watch, but they actually managed to stay awake until past 10 p.m.