Jay Leno has been hosting The Tonight Show since 1992, when Johnny Carson retired. He gave up his seat in 2009 to Conan O'Brien, but famously (infamously?) took the show back when The Jay Leno Show bombed. Leno has a contract with NBC through 2014, when he'd be 63—Carson retired at age 66.
Unnamed sources are telling The Hollywood Reporter that Jimmy Kimmel's move to 11:35 could force the network to edge out Jay. Kimmel does well in the 18-49 demo, and even beats The Tonight Show sometimes. "The more time Jimmy Kimmel is in that slot, the more the young audience goes that way, the harder it is for Jimmy [Fallon] to keep that audience," the source said.
NBC's play would involve moving Jimmy Fallon to The Tonight Show at 11:35 next summer before a "formal fall kickoff." David Letterman's contract with CBS is up next year, too, and executives are reportedly worried they could lure the popular Fallon over to the other network (Kimmel is on ABC).
The source also pointed out that if NBC announces the change early next year, they could reap the advertising and viewer benefits of a Leno farewell tour. NBC's only comment? "We do not speculate on rumor."