David Letterman celebrates his 65th birthday today. For those who can recall Letterman’s early years as a goofy, youngish guy in a sport coat, that milestone may come as something of a shock. He’s been a part of late-night TV for 30 years.

”Late Night With David Letterman” debuted on NBC on Feb. 1, 1982, with Bill Murray as the first guest. Murray returned to mark the anniversary this past Feb. 1 on “Late Show With David Letterman,” where Dave has held court on CBS since 1993.

It would be easy to focus on Letterman’s age and long run. But they somewhat obscure the fact that, with a couple of exceptions, nobody on late night is a kid. Jay Leno turns 62 in a couple of weeks. Jon Stewart and Craig Ferguson turn 50 this year, and Conan O’Brien will do so next year and Stephen Colbert the year after.

It’s interesting to note that Johnny Carson, the legendary template for all talk show hosts, took over “The Tonight Show” when he was 37. Chelsea Handler and Jimmy Fallon are 37. Jimmy Kimmel is 44. Their comparative youth may explain some of their success.

l A lost engagement ring sets up a proposal re- enactment on the season finale of “Up All Night” (8:30 p.m., NBC). This show has not yet been renewed for a second season.

Tonight’s other highlights

• John Goodman guest-stars on “Community” (7 p.m., NBC).

• A contestant goes home on “American Idol” (7 p.m., Fox).

• Michael takes the initiative on “Missing” (8 p.m., ABC).

• Liz tries to make Jack show he cares when his mother (Elaine Stritch) is hospitalized on “30 Rock” (8:30 p.m., NBC).

• The machine churns out too many names and numbers on “Person of Interest” (9 p.m., CBS).

• A reluctant party-planning staff digs in its heels on “The Office” (8 p.m., NBC).

• Martin encounters a grieving woman bent on revenge on “Touch” (8 p.m., Fox).

• Owen comes clean under duress on “Grey’s Anatomy” (8 p.m., ABC).

• Laura Innes (“ER”) guest-stars on “Awake” (8 p.m., NBC).

• A client’s Rolodex threatens to rock the nation’s capital on “Scandal” (9 p.m., ABC).

• “Independent Lens” (9 p.m., PBS, check local listings) presents “When the Drum Is Beating,” a look at Haiti’s rich musical tradition.