Fallon’s ‘Tonight Show’ holds on to Leno viewers

“The Tonight Show Starring Jimmy Fallon” turned a month old Monday.

So, how is “Tonight” doing?

This launch has exceeded even NBC’s expectations, and considering the recent fraught history with “Tonight Show” transitions, that means a lot.

Last week’s “Tonight” was seen by an average 4.5 million viewers at the regular 11:35 p.m. time, compared with 4.9 million for Jay Leno’s last full week on the air. And this number: “Tonight” has nearly double the audience of second place “Jimmy Kimmel Live!” and “Late Show With David Letterman.” Of vital importance, at least for NBC: Fallon’s “Tonight” is attracting more younger viewers than its competitors, far more than Leno’s “Tonight.” Youth wins the game in television, and “Tonight” is running up the score.

Have Leno’s viewers remained onboard?

So far, yes. NBC is completing proprietary research to determine precisely how many Leno loyalists have remained, but the network believes the majority have. This is a key metric, because the bottom fell out from under Conan O’Brien’s “Tonight” fairly quickly in 2009 after these viewers abandoned his show (many of whom went to “Late Show With David Letterman, which is not happening this time).

What is the age of Fallon’s viewers?

The average age is 54, or five years younger than Leno’s viewers, and “Late Show’s,” which now has the oldest audience profile in late-night TV. (“Tonight” is also a year younger than “Jimmy Kimmel Live’s” audience.) Again, youth rules in late night, or at least rules with advertisers — a key reason Fallon hosts “Tonight.”

What does the boss think?

Ted Harbert, chairman NBC Broadcasting, said in a recent interview, “I have an odd relationship with A.C. Nielsen, and deep in my heart get superstitious (when predicting ratings). I thought we could run the table with both Jimmy and Seth (Meyers, whose ‘Late Night’ is also doing very well), but we didn’t think it would be this high.”

What does the Newsday critic think?

Fallon’s “Tonight” is excellent, also refreshing, comfortable and often surprising, which are words seldom heard with regard to late-night TV. All key elements click — the monologue, especially, as well as the many comedy bits that made the hop from 12:35 to 11:35 with Fallon. Fallon and NBC promised Fallon’s “Late Night” would morph to his “Tonight,” but how many times are promises kept in this business?

Harbert puts it this way: “The mistake we made at this network (in 2009) is that a lot of time was spent telling Conan how his show should change.” But with Fallon, “all of us said, ‘You’re not going to have the network telling you what to do and screw it up.’”

Has the late-night landscape changed with the advent of Fallon?

The better question is, “What about Dave?” Letterman turns 66 on April 12, and while he may be the second-greatest late-night talk-show host in TV history, he’s now also second-oldest (Johnny Carson was 66 when he retired in 1992).

Letterman, who has a contract through 2015, has given no indication he plans to step aside, but the day will come, and possibilities to replace him remain the obvious ones: Stephen Colbert’s contract at Comedy Central ends this year, Jon Stewart’s next, but there now seems to be growing consensus that Colbert may now be the heir apparent. The average age of “The Colbert Report” viewer, by the way, is 43.