ASTONISHINGLY, “Monty Python’s Flying Circus,” the groundbreaking BBC comedy series, is 40 years old this year, almost as ancient as the Beatles. As Terry Jones, one of the six-member troupe who created and acted in the show, said recently: “Time just seems to get quicker. You look in the mirror in the morning and you think, ‘I’m already shaving again!’ ”

The principals are all in late middle age now, jowly and graying, and have in some ways become the very sorts of people they used to poke fun at. Michael Palin makes travel documentaries. Mr. Jones makes documentaries and writes scholarly books about the Middle Ages, the period the Pythons so memorably sent up in their film “Monty Python and the Holy Grail.” Terry Gilliam, animator turned filmmaker, is still quixotically obsessed with making a movie about Don Quixote. Eric Idle, who’s mostly responsible for the long-running Broadway production of “Spamalot,” writes musical shows, many of them recycling Python material. And John Cleese, who at 70 is the oldest of the group, in addition to appearing in movies and sitcoms and making golf-ball commercials, sometimes turns into a cranky old buffer complaining about cultural decline and Britain’s tabloids. He doesn’t watch much comedy anymore. “As you get older you laugh less,” he says, “because you’ve heard most of the jokes before."

The show, on the other hand, hasn’t aged a bit. In the United States, “Flying Circus” didn’t catch on until 1974, when it was pretty much off the air in Britain and the members had started to go their separate ways. Hugh Hefner was an early fan. Go figure.

But the show has had a surprisingly durable afterlife in this country, giving rise to second and third generations of fans who watch it on DVD and on YouTube, where it’s so popular it now has its own dedicated channel. Mr. Cleese said recently that in England he is far better known these days as Basil Fawlty, the title character in his post-Python series “Fawlty Towers,” than for his role in “Flying Circus.” But even in American middle schools now, there’s often a smart aleck or two who can do Mr. Cleese’s Silly Walk and know the Dead Parrot sketch by heart. When they get to high school in a few years they will also have mastered the sketch about the man with three buttocks and know all the words to the gay lumberjack song.