The young'uns have "American Idol" and "24," but what's on the tube for Grandma and Grandpa?

Networks define their success by the number of viewers they can attract between the ages of 18 and 49, also known as the "crucial” 18-49 demographic.

But with the Baby Boom generation now between the ages of 45 and 60 — and watching TV in large numbers — experts feel networks and advertisers will soon begin paying more attention to the older folks.

“The advertising industry is already beginning to see they may have been putting too many eggs in the basket of 18-34 or 18-49, and that those over 55 have been kind of ignored," said Professor Robert Thompson, director of the Center for the Study of Popular Television at Syracuse University. “Especially as baby boomers move into their older years, advertisers are going to realize this is an enormous category, that these are people who are still conspicuous consumers.”

Most networks do have a substantial base audience of older viewers, yet advertisers continue to prioritize younger demos.

Nielsen broadcast ratings and demographic data from the week of Jan. 9 through Jan. 15 show people ages 55 and over are watching shows like "Without a Trace," "Numb3rs" and "Law & Order" in significant numbers, in the neighborhood of 45 percent of the entire viewership for each show.

Shows like "NCIS," "Commander in Chief" and "Dancing with the Stars" are each watched by about 16 million people, exactly half of which are seniors age 55 and over, according to Nielsen.

“Senior citizens don't necessarily always want to watch shows about other senior citizens,” said Thompson. “They can enjoy watching things about pretty young people; not many seniors are dancing with the stars, but still that kind of program does well.”

But for some shows, success with the older folks can be the kiss of death.

"Commander in Chief" is going on hiatus, it was announced this week — often a bad sign for a program. According to the Pittsburgh Post-Gazette, “Commander in Chief” suffered in the ratings against the season premiere of "American Idol," and has never been strong among younger viewers. In fact, The Hollywood Reporter notes the median age of the show’s viewers is 54, making it ABC’s second most popular show among seniors.

Another popular show among seniors, the WB’s "7th Heaven," which according to Nielsen Media Research is watched most by ages 25-54 (45 percent) with its second highest demo being ages 55 and over (25 percent), ends its epic run this year, due to monetary constraints.

On the same network, a comedy called "Just Legal" pairing '80s star Don Johnson with a junior counterpart in 23-year-old Jay Baruchel was pulled after only two episodes and quickly cancelled when execs realized the show was attracting women ages 55 and over.

"Networks do not normally highlight the older viewers in their audience,” said Laura James of Nielsen Media Research. When asked why, James said, “It’s just not the usual selling demo.”

And with their favorite shows going off the air, seniors are turning largely to cable TV.

“A lot of the programs on cable are things that are already familiar to older viewers and that they feel more comfortable with, rather than the new shows being offered on broadcast,” said Bill Carroll, VP/Director of Programming for Katz Television Group, a media-buying firm.

The Hallmark Channel, for example, is bringing back popular stars from the last 30 years in monthly TV movies — actors like Richard Chamberlain, Shelley Long, "Happy Days" mom Marion Ross, Patrick Duffy and Loni Anderson.

At a recent press tour Ross, 77, remarked to a Canadian newspaper, “Hallmark is smart enough to realize that people our age are home, watching TV.”

An aggregate of senior citizens over age 65 at Sunrise Assisted Living in Paramus, N.J., revealed that of the two or more hours per day they watch television, most of it is on cable rather than network TV, except for syndicated programs like "Dr. Phil" and "Jeopardy."

While they say they like to stay in tune with current shows, none knew of "24," "Desperate Housewives," "House" or "Grey’s Anatomy."

It’s difficult, they said, to keep up with shows that need a lot of weekly attention, but they do enjoy shows like "The West Wing" (also recently cancelled due to falling ratings) and "ER."

Many admitted they miss sitcoms and "the older shows" like "Andy Griffith," "Gunsmoke" and "Bonanza" and variety shows like Sid Caesar's "Your Show of Shows" and "The Carol Burnett Show," most of which are available in reruns on cable. What they do wind up watching is A&E, AMC, TBS, TNT, ESPN and of course — reruns of "The Golden Girls," which is still popular in syndication.

Nielsen data show the programs watched to a significantly lesser extent by people ages 55 and over are "My Name Is Earl," "Fear Factor," "Wife Swap" and "The Office."

But as long as these shows hit the target 18-49 demographic, they will continue to stay on the air.

“People 18-34, 18-49 are off doing a lot of other things besides watching television, especially network television. They’re messing around on the Internet or playing video games, watching DVDs… It’s a difficult demo to get and that makes them the most valuable,” said Thompson.

Advertisers will pay big for this group because they feel they have yet to establish their product preferences.

“Advertisers work on the premise that younger people haven’t established a brand preference yet — haven’t decided on a car, haven’t decided on a fast food restaurant, and that they are more likely to be influenced by advertising,” said Carroll. “Whereas older viewers have already chosen their brand of toothpaste.”

He added, “Younger viewers also have more discretionary income and are more likely to spend on impulse,” therefore making them more impressionable to advertising.

Thompson agreed that the younger set has more cash to blow — and more need to blow it.

“The reason why you’ve got this big baby boomer population yet the 18-49 group still remains desirable is that people in that age group are still on the make,” he said. “Many aren’t married yet, so they care about fashion and clothing. Others are recently married and need SUVs, diapers and cleaning materials.”

Getting the customers younger pays off as people become more brand-loyal in their lives, Thompson added, “And there’s a lot of stuff you may not need as much as you get older.”

But with so many networks, rather all, angling for the young hipster, wouldn’t it make sense for someone to skew older and capture the niche?

NBC and ABC, to be fair, are both targeting the 25-54 audience. And according to media-buying company Magna Global, the numbers have suggested the majority that come to the couch in that demo have deep pockets.

Back at the Hallmark table of the TV press tour, Shelley Long and Patrick Duffy told the Canadian paper The Edmonton Sun that they too believe the networks will sway back to older actors and older audiences.

“It just has to happen before we’re dead,” Duffy said.