"I'm awash in melancholia," Letterman tells the New York Times. "I'll miss it, desperately. One of two things: There will be reasonable, adult acceptance of transition. Or I will turn to a life of crime."
Letterman says he feels that the new era of late-night shows, marked by videos that go viral the next morning on the Internet "sneaked up on me and went right by." The realization that the late-night landscape has changed in recent years hit him when he watched John Mayer host an episode of "The Late Late Show" earlier this year, before James Corden took over for Craig Ferguson.
"He's young. He's handsome. He's trim," Letterman notes. "So then I realized, I got nothing to worry about. I know I can't do what Jimmy Fallon's doing. I know I can't do what Jimmy Kimmel is doing. There's nothing left to be worried about. It's all over, Dad, you're going to be just fine. You're going to a new place. They'll be very nice to you, Dad. You'll make a lot of friends."
"I'm 68," he continues. "If I was 38, I'd probably still be wanting to do the show. When Jay [Leno] was on, I felt like Jay and I [were] contemporaries. ... I thought, this is still viable -- an older guy in a suit. And then he left, and I suddenly was surrounded by the Jimmys."
Letterman's successor, Stephen Colbert, is scheduled to take the reins later this year. Letterman said he was not part of the decision to hire Colbert as his replacement , but certainly held opinions about who should take over and was initially miffed that CBS didn't consult him. "I always thought Jon Stewart would have been a good choice," he tells the Times. "And then Stephen. And then I thought, well, maybe this will be a good opportunity to put a black person on, and it would be a good opportunity to put a woman on. Because there are certainly a lot of very funny women that have television shows everywhere. So that would have made sense to me as well."
Though he hasn't offered any advice to Colbert, Letterman says he's confident that the "Colbert Report" host "will add a third, different dynamic" against Kimmel and Fallon.
And, he says, his last show will be "cheery."
"I want it to be upbeat, and I want it to be funny, and I want people to be happy that they spent the time to watch it," Letterman tells the Times. "Johnny [Carson]'s last show was historic. This one won't be. [Laughs] This one, people will say, 'Ah, there you go. When's the new guy starting?'"
Read Letterman's full interview with the New York Times here.