ANN ARBOR, Mich. — Every Friday night from September to May, at an off-campus nightclub in this thriving college town, a group of die-hard music fans gathers to dance to some of the most devoted live bands in southeast Michigan. There are women in skintight red dresses, long-haired men sucking down bottles of beer and couples flirting in the alcove outside the bathrooms.

In fact, just one thing distinguishes the crowd from nearly any other rock-and-roll show in a small city in America: Almost everyone is over 60.

OK, two things: The show always starts at 6:30 p.m. and ends at 9 p.m., in time to get to bed at a reasonable hour.

The party’s official name is “Ann Arbor Hour Happy Hour at Live,” but many people call it “Geezer Happy Hour,” “Geezer Dance Party,” or just “Geezers.” It’s organized by Randy Tessier, a 72-year-old University of Michigan lecturer and writing instructor who has played in rock and jazz bands since he moved to the city in 1972, back when it was a patchouli-scented center of American counterculture.

From his windowless office in Angell Hall, festooned with posters of Karl Marx, Miles Davis and Jimi Hendrix, Mr. Tessier books bands and runs the group’s 2,700-strong Facebook Community page.

“I call us the silver tsunami,” Mr. Tessier said. “There’s a lot of us and we still want to rock.”

“Geezer Happy Hour” is the latest iteration of a weekly, musical happy hour that has been happening off-and-on — mostly on — since it started in the early 1970s at a one-room bar called Mr. Flood’s Party. Over the years, the crowd has aged right along with the acts; some people have been coming to the shows for 50 years.

The turnout on a recent Friday night was typical: a convivial mix of finely-preserved hippies, activists, professors, townies, amateur musicians and an assortment of more than 100 other folks over 60 who simply cannot stop dancing.

They were dressed with unselfconscious flair: There were fringed jackets and fedoras, western shirts and bowties, rainbow bandannas and braided beards.

Also, there were earplugs, and a walker or two.

“All of the people got older and they’re still here,” said Tom Kenny, a happy-hour long-timer wearing a purple tie-dye shirt and round, John Lennon-style glasses.

Over the years, the happy hour has wandered downtown from venue to venue — the Blind Pig, the Cavern Club, the Heidelberg — before settling at the generically named Live in 2013. The musical acts range from the almost-famous (two members of Sky King, which put out a record on Columbia in 1975, played the recent show) to the famous-for-the-night. They play rock, blues, soul, jazz and country: anything that gets the crowd moving, which isn’t very hard.

“It’s beautiful,” said Dan Mulholland, a longtime Ann Arbor musician. “These people will dance to anything.”

Mr. Mulholland, who was dressed in classic rockabilly style in head-to-toe denim, plays gritty rock music that recalls hard-edged Michigan legends like the Stooges and the MC5. (Mr. Mulholland said he knew a young Iggy Pop.)

When Mr. Mulholland first performed at the Geezer Happy Hour, he said, he was taken aback by all the bluehairs. “But then I looked in the mirror,” he added, and realized that he was 73 himself.

Among the dancers on the recent Friday were Judith Cawhorn, 76, and George Fahmie, 84, both retired. They first met on Match.com in 2010. Ms. Cawhorn had been going to the happy hour for years, and she didn’t want to tell Mr. Fahmie about the party until she knew he could really dance. (“He was so much older than me,” she said.)

So on their first date, she put him through the paces at another bar. Mr. Fahmie passed. Now Ms. Cawhorn calls him “my sweetie,” and the couple was among the first on the dance floor and the last to leave.

“Most people are dead at my age,” Mr. Fahmie said. “But tap twice on the table and I’ll get up and start dancing.”

“It Is the Most Wonderful Thing in My Life”

The staff of Live, which transforms into a bottles-and-tables dance club for young professionals around 10 p.m., adores the elderly crowd.

“They have the most fun,” said Chelsea Anderson, a 31-year-old bartender, who has been working the happy hour for 6 years. “Everybody loves each other. It’s a stark difference from the late crowd, where everyone is upset and barfing.”

Plus, Ms. Anderson said, the happy hour regulars are “creatures of habit” who rarely change their drink orders; the only downsides, she added, are that they lose stuff a lot and have, on a few occasions, needed an ambulance.

That night, dressed in a star-spangled T-shirt and jeans, Mr. Tessier played bass and sang in a five-piece band of veteran local musicians. The crowd was especially excited to see Peter Madcat Ruth, a virtuosic, Grammy-winning harmonica player. Over two sets, the group tore through twenty songs, including the Beatles’ “Ticket to Ride,” the Meters’ “Cissy Strut,” and Santana’s “Samba De Sausalito.”

“They’re the top elite of the Ann Arbor rockers,” said Corky Wattles, 66, a retired car salesperson.

Between sets, Ms. Wattles and about a dozen other people ambled out onto South First Street to get stoned.

Ann Arbor has been synonymous with marijuana activism for a half century. A December 1971 rally to free the activist John Sinclair — Mr. Tessier’s friend — then serving a ten-year prison sentence for possession of two joints, drew 15,000 supporters, who watched Mr. Lennon and Stevie Wonder perform, and Bobby Seale and Allen Ginsberg speak. Four months later, after the Michigan Supreme Court ruled the state’s felony cannabis law was unconstitutional, revelers held the first-annual Hash Bash (like Mardi Gras, but for weed) on campus.

“We’ve been doing this for 50 years,” said Ruby Butler, 73, between pulls off a small glass pipe. “Only now, it’s legal!”

Since Michigan voted to legalize marijuana for recreational use in 2018, dozens of dispensaries have opened in Ann Arbor — an irony not lost on a generation of crinkly-eyed ex-student activists. Ms. Wattles, sharing a joint, pointed out that the drug was great for seniors, who use cannabis to treat conditions including arthritis and insomnia.

Also among the tokers was Griff Griffin, 70, a retired computer consultant who described himself as a modern philosopher. Mr. Griffin wore a multicolored peace sign necklace, and a single, straw-colored dreadlock that he said he hadn’t cut since the start of the first Gulf War, in 1990.

“It’s the only thing that keeps growing,” he said.

For its devotees, the Geezer party isn’t just a link to the past, but a sustaining communal ritual. Ms. Wattles refers to its members as her “tribe” and the event itself as the “church of dance.”

“It is the most wonderful thing in my life,” said Maggie Levenstein, another regular. “It makes me happy every single week.”

Dr. Levenstein, 60, an economist at the University of Michigan and the head of the Inter-university Consortium for Political and Social Research — the world’s largest archive of digital social science data — works with data from the University of Michigan Health and Retirement Study. She has a wonk’s perspective on the benefits of all that dancing and smiling.

“They are active and they have a community,” she said. “It is all the things people know are important to healthy aging but no one individual person could create on their own.”

During the long pandemic lockdowns, Dr. Levenstein set up weekly Zoom sessions at the regular Friday time. Someone piped in music from Spotify. As many as 70 people at a time logged on to dance remotely.

Among the only downsides of the older community, Ms. Wattles said, was that there weren’t enough single men — though there was one guy whom she called “the creeper.”

“He zeroes in if any single woman makes eye contact with him,” said Ms. Wattles.

Back inside the club, under a disco ball, the dance floor was packed. Someone had distributed glow sticks, which people were waving in time to the music. No one in sight was looking at their phone — a fact some in the crowd regarded with generational pride.

“I can’t hang out with kids because they live in their cameras,” said Angela Todd, 75, a gravelly-voiced woman with long, white-blonde hair. “They don’t tap a finger or a toe. They don’t feel music at all.” Two young men, who showed up early for the D.J. set that would start later on, sat politely in chairs by the entrance, looking confused and impressed.

At 9 p.m., the band finished with “Gimme Some Lovin’” by the Spencer Davis Group. By 9:30 p.m. most of the revelers had left, hugging and kissing on the way out the door. Some were headed to Zal Gaz Grotto, an old Masonic social club on the west side of the city, where the dancing would continue until 11 p.m. But not Mr. Tessier. On stage, his band was breaking down its equipment. The player-coach looked jubilant but exhausted.

“I’ve been married three times,” said Mr. Tessier. “I learned a long time ago to go straight home.”