Younger viewers are fleeing TV at an accelerated pace.

The trend should surprise no one who has seen the rise of Netflix, a resurgence of video games and a shift to digital. But new Nielsen data show a widening gap in viewing behavior among young and old that's alarming some network executives.

For the four weeks ending Oct. 28, coinciding with the start of the official TV season, the number of people ages 18 to 34 using TV has plunged 15% and is down 36% from 2014. The drop-off among teens – 18% from last year and 48% since 2014 – is even more pronounced.

"It looks like a big, daunting number," says Peter Katsingris, senior VP of audience insights at Nielsen, and marks a sharp contrast with the mere 2% drop from 2017 among folks 55 and older, the most loyal viewers. But he says it reflects the new millennial mindset.

"Younger generations are growing up with more choices at their fingertips," he says. "They don't know that you had to watch at 3 o'clock on a Wednesday if you wanted to see a show." For them, dependency on a network schedule is "like looking at a typewriter."

In fact, the very definition of TV watching has changed. A broader measure of television usage that includes streaming through any device connected to a TV – but not websites or mobile apps – shows a less worrisome 5% yearly drop.

And, as often happens, executives question the reliability of Nielsen data, suggesting it could prove another statistical blip. But all signs point to contrary evidence: For the three months ending Sept. 30, cable and satellite systems reported the loss of another 1 million customers, the largest quarterly drop yet. (About 40% of homes led by millennials don't subscribe to cable or satellite services.)

Brian Hughes, executive VP at ad firm Magna, projects that 47% of the video watched by the 18-to-34 crowd is streaming, up from 41% last year and 21% in 2014, and he expects the figure to top 50% in 2019.

For CW, which targets the audience that's bailing from TV schedules, "multiplatform" viewing over a longer time span "has always been part of our business model," says network president Mark Pedowitz. But that pace is accelerating.

Close to half of the "Riverdale" audience is online, on CW's own app and website, and for the new "Charmed" remake the figure is 40% to 45%, he says. ("The Flash" is also among its most heavily streamed series.)

MTV is responding to the declining usage among its core audience with a 36% boost in original programming since 2016, using lower-cost shows produced in-house, which has led to ratings increases. As an insurance policy, the network also has shifted its target audience – once the most fickle 12-to-34 age group – to seek 18-to-49-year-olds with shows including a revival of 2009 reality series "Jersey Shore."

"We flipped the strategy," says Chris McCarthy, president of MTV and sibling channels, who now sees it as a "youth-culture brand" rather than a TV network. And MTV no longer even wants its TV for some projects: Last month it signed a deal to relaunch reality series "The Real World" on Facebook Watch, and it plans similar online revivals of former shows including "Aeon Flux," "Daria" and "Undressed."

"We're turning streaming viewers into our new customers," he says.

But other programmers have hastened the decline by selling reruns of their shows to Netflix and other streaming rivals, who are using them to steal viewers. Two-thirds of all TV homes in the USA now subscribe to Netflix, Amazon and/or Hulu. That's why Disney and Warner Media are belatedly planning streaming apps of their own.

"Many networks are going to be under stress to adapt, and some are not going to make it," predicts Kevin Reilly, president of TNT and TBS. "I think it's going to be a very tumultuous time with the fraying of the audience" as fewer viewers translate to lower ad revenue, the lifeblood of the traditional TV business.

Shows like NBC's "The Good Place" and ABC's "A Million Little Things" have modest ratings on TV but gain a substantial portion of their young-adult viewership over time on digital platforms.

Hughes says advertisers should be "smarter about how we reach younger people" on traditional TV or "be more cool with targeting older demographics than we used to," a refrain often heard from the likes of senior-skewing CBS.

Some executives hold out hope that younger people will mimic their parents' behavior as they age and return to TV. But others aren't buying it, and the pace of technological change argues against that behavior.

"They were born swiping," Reilly says. And that may translate to fewer shows from media companies. "At a certain point, if you're feeling economic stress, you're doing more with less," he says.

So-called peak TV, with "dozens of networks making big bets on dozens of shows, will be pared back. But the viewer won't be robbed, because in this landscape there's too much to watch anyway."