Are TV advertisers missing the baby boomer boat? -- Network audiences are older than ever, but you wouldn't know it from the commercials

After watching her favorite show, Desperate Housewives, it’s not uncommon for divorced L.A. real estate agent Kathy Gardner to blow a sizable portion of her $150K-plus earnings on trendy jeans, shoes, and haircuts so she’ll look like her favorite character, Susan. That’s what advertisers like to call disposable income, a.k.a. the Holy Grail of Madison Avenue.

Trouble is, Gardner is 51 — two years outside the mouthwatering 18-49 demo. To the rest of the world, 50 is the new 30. To Madison Avenue, Gardner and her baby-boomer compatriots might as well be invisible. Currently, advertisers will pay a reported $172,000 for an ad during the No. 77-ranked The O.C. (which attracts viewers with an average age of 30.5), while paying just $133,000 for a spot during NCIS (average viewer age: 55.3), which is often among the top 10 shows on TV.

Despite all that stuff about the shorter attention spans of twentysomethings, advertisers still cling to the conventional wisdom that if they grab TV viewers early, they’ll become brand-loyal for life. Madison Avenue ”has always been obsessed with youth,” says Janie Curtis of Frank About Women, a consulting firm that is trying to reverse the trend by urging advertisers to target female boomers. ”The younger demo is cooler, hipper, and reflects more positively on a brand.”

And that’s just too bad for nets like NBC, since even an unqualified success like Medium isn’t attracting enough of that demo. While total TV viewership is up 2 percent (a good thing), the coveted 18-to-49 demographic is down 3 percent. Just how old is the average viewer? NBC’s is now 49, up from 46.4 last year; ABC’s at 46 (up from 45); CBS can’t get any younger than 51.6. Even Fox and The WB (which abandoned the Clearasil crowd last year) are at a relatively mature 45 and 37, respectively. And we’re betting those numbers will only go higher as the entertainment universe expands and more young viewers — particularly males — opt for cable offerings like Adult Swim or the Internet or videogames. (Something the movie industry can certainly relate to.)

If it weren’t for the advertisers, say the networks, all would be fine. And they do seem to be adapting: As viewers have grayed, so have the shows. TV’s biggest hits feature a cavalcade of middle-aged actors: William Petersen (CSI), Hugh Laurie (House), Felicity Huffman (Housewives), Anthony LaPaglia (Without a Trace) — we could go on. This season proves even younger stars don’t make a difference: The average viewer for CBS’ Friday-night lineup, which includes Ghost Whisperer starring Jennifer Love Hewitt, is 53.

”We’re attracting more viewers but our median age is not going down substantially,” says CBS’ head of research David Poltrack. ”Are we supposed to be punished for having a higher median age? This is the boomer population that fuels the economic engine for this country. They shouldn’t be considered a negative.”

And they’re not?as long as they watch TV at the same time as their kids. Shows like CSI can command hefty ad rates ($478K) because they also perform well with younger viewers. But shows that skew older, like ABC’s Commander in Chief — the most watched new show of the season, whose average viewer happens to be 54?are inevitably mocked by Madison Avenue and the press. (Confession: EW once referred to CBS as ”the go-to network for Depends commercials.”)