If CBS wanted to use the opportunity of David Letterman's 2015 exit to age down its audience, Stephen Colbert is one of just a few candidates with a proven track record for drawing in the ideal demographic.

As host of Comedy Central's Colbert Report for eight years, Colbert has seen a strong and steady showing among the advertiser-coveted adults under 50 -- all while broadcast competitors have steadily dropped.

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Yes, there are exceptions. Jimmy Kimmel's ABC shift to the earlier 11:35 p.m. time slot has lifted his showing. And the recent Jimmy Fallon takeover of NBC's Tonight Show has exceeded expectations. The latter continues to rake in the most adults 18-49 (by a wide margin) two months into his run, surprising analysts and throwing the perennial late-night hierarchy out of order.

The Colbert Report currently ranks third in adults 18-49 across all of late night -- behind Tonight and The Daily Show With Jon Stewart -- but it has the youngest-skewing audience of any late-night broadcast or cable show (excluding TBS' lesser-watched Conan) with an average age of 42.3 years. Letterman's average viewer, by stark comparison, is a whopping 58.2 years old. The comparatively young crowd, should it make the move with Colbert, would give CBS a big advantage over NBC and ABC. Their late-night efforts are bringing in respective averages of 57.1 and 54.3 years old.

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"They're going to take the opportunity to try to make their daypart younger," Sam Armando, senior vp and director of strategic intelligence at media-buying firm SMGx, told The Hollywood Reporter after news of Letterman's departure. "If you're going to make an effort to age down a bit, you're not just going to do it with a host that's 38-40 years old. You're going to have to change the format a bit. CBS is getting a blank canvas."

The look of that canvas is now taking shape. The choice of Colbert puts CBS in direct competition with the younger-skewing, viral-video-prone Fallon and Kimmel. Sources tell THR that the network moved quickly in locking down Colbert, knowing his and Letterman's deals synced and that Comedy Central would make a play to keep the host on board.

And Comedy Central had every reason to want to keep Colbert. Though cable offers a traditionally smaller mouthpiece, Colbert's reach there has been extensive. The combination of The Daily Show (a close average age of 43.2 years old) and The Colbert Report has been one of its biggest bragging points for years. Prior to the anomaly of Tonight's Fallon surge, the duo ranked as the top two talkers in adults 18-49 across all of TV. (And when the revamped Tonight ultimately settles, they likely will again -- at least until Colbert's departure at the end of 2014.)

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Stewart and Colbert also gave Comedy Central the most organic pairing on late night. Colbert got his break on The Daily Show, and the two telecasts often bleed into one another. The duo's chemistry and camaraderie won't be easy to replace on Comedy Central -- especially with John Oliver now at HBO and out of the picture.

"When you talk to Comedy Central, they will always mention that combo of Colbert and Stewart," adds Armando. "I think the viral opportunity he provides and the extensions in books and commercials … those lend themselves to promoting the network indirectly and directly. He's a big part of their identity."