Playwright John Fenn was expounding righteously about the evils of gerontophobia — the fear or hatred of aging and old people. His polemic came in the context of a discussion about his new musical comedy, “The Geriatrical Theatrical: Celebrating the Chronologically Enriched,” and Fenn was arguing for the capacities of the aged brain, the joy of senior fellowship and the vibrancy of his cast and collaborators. Why, five of the eight people at the rehearsal table were older than 70 and Fenn proudly announced that he was the senior player at age 79.

But no sooner were the words out of Fenn’s mouth than he leaned forward and grimaced at a reporter taking notes. “Now, you don’t have to push that around in the media,” he said.

Composer Drew Jansen, who wrote the songs for this new musical, quickly jumped in.

“Why? Are you afraid of your age, John?” he said. “Are you chronophobic?”

And so goes another vignette in the human shadow dance with aging. Are you 79 years old or 79 years young? Are you getting older or getting better? Are you really only as old as you feel? Does life begin at 60 — or as director Bain Boehlke said during a group interview, at 80?

Fenn and Jansen’s new musical, which opens at Plymouth Playhouse under Boehlke’s direction, is aimed at people who want to feel good about their age — whatever it is.

Jansen was the only one younger than 65 when the cast and creators sat down the other day to talk about the comedy. Dee Noah thought it was so charming that this youngster had written a song called “Not Dead Yet,” in which Jansen’s lyrics point out that every ache is proof that you’re still here.

“These are issues for older performers,” Noah said. “This work is incredibly physical, and you don’t recover as quickly.”

When the topic of memorizing lines came up, the murmurs got loud and knowing. Actor Claudia Wilkens volunteered a story of a production several years back in which she went completely blank during a performance.

“It was not a happy day,” she said, able to laugh but still clearly nursing the mental bruise.

“Theater is unforgiving on the memory plane,” Boehlke said.

Out of real life

“Geriatrical Theatrical” originated seven years ago, when Fenn’s wife, writer Jill Breckenridge, suggested they look at moving into Becketwood, a cooperative for “independent senior living” in south Minneapolis.

“I resisted like crazy,” he said.

But move they did, and Fenn warmed to life among others roughly his own age. Certain experiences started to suggest theatrical scenes and characters to him, and then Fenn looped in Jansen, his collaborator on the musical version of “A Servant’s Christmas.”

They took their time and arrived at a scenario in which some oldsters decide to put on a musical comedy. One of them (Phil Ross) tries to cajole his crotchety brother (Richard Ooms) into playing along. Wilkens plays a dealer in the casino of life who lays down fateful cards — including a host of prominent ailments.

“You can’t control the hand you’re dealt,” Jansen said. “We can control how we react.”

Show biz getting older?

Theater remains largely a younger person’s game (except for audiences), but “Geriatrical Theatrical” plants another flag on the turf of senior artistic expression. In 2008, 84-year-old Charles Nolte headlined “Exit Strategy,” a play by Bill Semans and Roy Close about denizens of an old people’s home who plan a heist. Choreographer/director Michael Matthew Ferrell has a group of senior singers huffing and puffing in “Alive and Kickin,’ ” with regular musical revues. We likely will see more of this stuff as the baby-boom cohort edges into the 60s and 70s (and we aren’t talking about those radical decades).

Fenn said that he and Jansen want seniors to watch the show and shed the stigma that American society stamps on aging.

“So many old people internalize this feeling,” Fenn said. “We’re saying to the chronologically enriched that you’re not going downhill, you’re going uphill.”

That comment might not have come out quite like Fenn meant it to — indeed, life does start to feel like an uphill climb — but you can see his point.

Boehlke, who at 73 regularly directs and designs sets at the Jungle, suggested that physical limitations can be matched by experience and wisdom.

“Theater is an occupation that always renews itself,” he said. “Theater lives at the heart of community. It’s always young, always vital. Who could ask for anything more?”