I don’t know which fact is more surprising (depressing?):

1. David Letterman is older than Johnny Carson was when Carson retired.

2. I’m older than David Letterman was when he began hosting Late Night.

When Johnny Carson aired his final Tonight Show in 1992, I had recently turned 14.  I was old enough to understand that Carson’s retirement was a big deal, although I couldn’t appreciate it on the same level that my parents could.

I’m also too young to remember a time when David Letterman wasn’t on the air.  He took over the post-Carson timeslot in 1982.  I initially became aware of Letterman first-hand during one of his early prime-time anniversary specials, since staying up even to 11:30, much less Late Night‘s 12:30, was a tall order for a kid in single-digits.

Letterman’s show was, in some ways, an evolution of—and a reaction to—Carson’s Tonight Show.  Some of that was by design, as the Carson team specifically forbade Late Night from mimicking certain elements that would have made the program too similar to Johnny’s.  For example, Letterman wasn’t allowed to do a lengthy, Carson-esque monologue, and Paul Shaffer’s “World’s Most Dangerous Band” could only be a four-piece, not a full orchestra like the Tonight Show had.

Coupling Letterman’s own creativity with the external pressure of Carson’s restrictions gave birth to the most innovative talk show ever, and the most innovative late-night program of any kind in history, with the possible exception of Ernie Kovacs‘ brief stint as the host of Tonight.

Letterman would be the first to admit that he could never be as good as Carson at what Johnny did best.  Dave wasn’t nearly as charming as Johnny Carson was.  He also didn’t have Johnny’s acting chops or more multifaceted background as a performer.  To wit: Carson had begun his entertainment career as a young magician, of all things, but he later gained experience as a game-show host and possessed musical abilities entirely beyond the scope of Letterman’s more finite skill set.

But that was the point.

Letterman, who idolized Carson, was doing something different.  He was acerbic and ironic and occasionally belligerent in a way that Carson could never be.  Letterman’s Late Night spawned comedy that was often absurd or minimalist, even going so far as to make an intentional mockery of the format.

Letterman’s “lesser” status compared to Carson, and the New York locale of his program, frequently left him without access to the same level of celebrity guest the Hollywood-dwelling Tonight Show could obtain on a nightly basis.  But that, too, was a weakness-turned-strength: Letterman was often at his most skilled when he was stuck with oddball minor celebrities like Brother Theodore or Harvey Pekar.

Whereas Carson could be folksy and playful and engaged with any guest, Letterman didn’t have half of Johnny’s ability to seem interested in his interview subjects.  This was all part of the fun, of course, as Letterman’s conversations with the likes of Shirley MacLaine or Cher created awkward laughs in an era when awkwardness wasn’t a primary source of comedy on television.

Letterman and his staff created a show that was years ahead of its time.  That might not even be accurate, since many of the things Late Night did would never be permitted by a network today.  Like inexplicably dubbing reruns.  Or slowly rotating the picture over the course of the hour.  Or harassing the Today Show with a bullhorn.

Late Night won the Emmy for Best Writing in a Variety, Comedy, or Music Program each of the first four years it was on the air.  It later won a fifth, and added a prestigious Peabody Award.

The Peabody put the show in a different category.  This was no longer merely a good TV program.  This was Culturally Relevant—capital “C,” capital “R.”  The show created a litany of memorable bits, from the Top Ten List to Larry “Bud” Melman to Stupid Human Tricks to pretty much everything Chris Elliott did.

Ultimately, Letterman’s unorthodox if brilliant segments and his penchant for scaring publicists probably cost him his dream of hosting the Tonight Show.  Jay Leno, an erstwhile favorite guest on Late Night, understood the business of comedy better than Letterman and famously won the right to succeed Carson, despite Carson’s preference for Dave.  Leno eventually claimed ratings dominance over Letterman’s Late Show.

Just as Carson did a generation ago, Letterman leaves at a moment in history when the rest of the medium’s late-night landscape has changed around him.  Letterman created a more modern, hip vision of what a talk show could be.  It was something qualitatively different than what Carson was doing.  On top of that, newcomer Arsenio Hall, while not in Letterman’s league when it came to pure comedy, was attracting an even younger demographic to late night.

Letterman’s show gave us an early glimpse of what the next wave of comedy would look like: A touch meaner, a little more self-aware, much more steeped in irony.  By the 1990s, Carson’s show was largely enjoyable as a nostalgia piece.  It provided a glimpse of the old master, still entertaining, if no longer at the height of his powers.  Part of the attraction at that point was the fact that the host was the last holdover of a nearly bygone era.

That’s where Letterman finds himself today.  Or, probably, where he found himself a little over a year ago, when Leno retired.  As he recently told the New York Times, Letterman was suddenly “surrounded by the Jimmys” when Leno finally stepped down for good.  It was no longer clear to Letterman whether the decades-old format of “the guy in a suit” made as much sense as it did in 1987 or 1995 or 2002.

Once the innovator, Letterman is now doing a show that seems quaint and conventional.  Just as Carson’s cozy, Hollywood-friendly philosophy gave way to Letterman’s wicked, almost satirical take on late-night television, Letterman’s “guy in a suit” has made way for audiences with shorter attention spans who watch everything with a smartphone within arm’s length.

Letterman’s Late Show isn’t based around generating viral, next-day content the way other late-night shows are.  Letterman’s replacement, Stephen Colbert, will undoubtedly be cognizant of this and do a much different show than the previous incarnation of the Late Show.

Even Jimmy Kimmel, who idolizes Letterman even more intensely than Letterman idolized Carson, employs a style that recognizes the need for YouTube-friendly bits that will meander through social-media pathways via everyone from your little sister to your grandparents.  Letterman doesn’t promote segments from his show using his personal Twitter account because Letterman doesn’t have a personal Twitter account.

Put another way, Letterman has gotten exactly what he always wanted: In every respect, he has become his generation’s Johnny Carson.

I can’t help but feel just a little sorry for younger Letterman fans whose first memories of Dave’s work are of the Late Show.  I reluctantly admit that, as good as he was on CBS, Letterman probably never quite reached the heights he did at NBC.

The most severe criticism—the most severe—I could lob at David Letterman is that, at some point over the last couple of decades, his show became merely “very good.”

After the first few years of the Late Show, when it became apparent that Jay Leno had a secure position in the ratings battle, Letterman settled into a more formulaic, less-ambitious routine.  Long a key part of his comedic arsenal, his sardonic wit seemed to ferment into genuine, uncomfortable bitterness at times.

He’s loosened up in recent years after finding fulfillment in his personal life, but the surprising truth is that the most memorable moments of the last 15-20 years have been non-comedic.  Meanwhile, much of the funniest material from the Late Show era aired in the mid-90s.

That’s why I hope that younger fans—and non-fans—will take advantage of the godsend that is YouTube and explore the mountain of Late Night and early Late Show footage.  I want them to understand that, for a time, Letterman’s program transcended being just a television show.  It meant something.  As much as any show of its kind ever could.

The shame of it is that Letterman’s contentious exit from NBC left some bruised egos on both sides, and, barring some secret, behind-the-scenes, intellectual-property miracle, the first third of Letterman’s contribution to television will remain locked in a vault as he airs his final show this evening.

Even this is a parallel to Carson, I suppose, as the archaic practice of “wiping” old tapes cost Johnny Carson nearly all footage of his first eight years behind the Tonight Show desk.  The difference, though, is that Carson probably hadn’t quite hit his stride in 1970, whereas much of Letterman’s best work—and certainly his most groundbreaking work—may never see the light of day on network television ever again.

His time at CBS has been uneven.  While no one is as good when Letterman is at his best, those “bests” didn’t come as consistently after the heartbreak of losing the Tonight Show, the literal heartbreak of major cardiac problems that necessitated bypass surgery, the perspective-gaining experiences in his personal life, and some embarrassment brought on by the revelation of having secret relationships with several female employees.

I almost never missed an episode over the last few years of Late Night and the first few years of the Late Show.  Eventually, it became just another show that I would try to catch when I could.  Like the Tonight Show in its latter days, it was still good, but it wasn’t necessary the way Late Night was.  Even in the glorious, tape-free, time-shifting age of DVR, I would seldom record and/or watch after I hit 30, sometimes only in search of the television equivalent of comfort food.

That brings me back full circle to Carson and his parallel to Letterman.  When Carson took his final bow in 1992, he had been hosting the Tonight Show for 30 years.  He had been a fixture in popular culture since my parents were children.  He was a constant.  Familiar.  A tether to a bygone era.  And to youth.

That, in the end, is why Letterman’s departure is so meaningful.

As I said, I cannot remember a time when David Letterman did not have a nightly television show.  Whether his last decade has been as innovative as his first is irrelevant.  He is a true giant, not just in television, not just in comedy, but as a cultural touchstone of the past three decades.  His humor shaped the comic sensibilities of a generation.  He has remained funny as that generation grew up, found careers, got married, had children, and began to enter middle age.

Generation X and older Millennials may not fully understand what David Letterman’s retirement means to them until sometime Thursday night, when they flip over to CBS and they’re greeted by a random rerun of The Mentalist.

Then, they’ll feel it.

We’ve gotten a glimpse of what this loss means through others, though.  Last week, Norm MacDonald made his final Late Show appearance.  After completing his five-minute set, MacDonald struggled to maintain his composure as he recounted the story of the first time he ever saw David Letterman perform.

MacDonald repeated a joke he had heard Letterman tell that night in Toronto, when Norm was just 13 years old.  In the end, fighting just to get a few words out, MacDonald confessed what so many of us are reminded of now, concluding: “I love you.”

Jimmy Kimmel had a similar tribute on his own show last night.  He not only thanked Letterman for the inspiration that led Kimmel to his own late-night success, but also openly told his viewers to watch Dave’s show tonight, not his.

Jimmy and Norm get it.

Who knows what that final show holds?  I’d love to see surprise appearances by Kimmel, to offer a (possibly unauthorized, probably tearful, definitely funny) tribute, and by Jay Leno, to bury the hatchet once and for all and repair a once-strong professional relationship.

And, hey, maybe Andy Kaufman will show up, too.

The world has changed so much in 33 years.  While Letterman remains—for one more night, anyway—much of what held cultural significance back then has naturally eroded, died, or been replaced.  To cite one of a thousand examples, I wouldn’t have had to worry about avoiding online leaks of final-show details tonight if it were still the 80s or 90s.

But that’s what I’ll do.  Total blackout on my end until 11:30.  Because I want this last show to be experienced as it should be: Moment-to-moment, as it happens.  No hashtags.  No spoilers.  No trending topics.  No live-tweeting.

Just the viewer and the medium and one final hour with the funniest man on television.