It seems unlikely that when Amy Herzog started work on her 2011 play 4000 Miles she was trying to prove the old axiom that youth is wasted on the young.

Although the production of 4000 Miles at Shaker Bridge Theatre in Enfield is well-acted and thoughtfully directed, three of its four characters are so young and unformed that they function as unreliable narrators. If they don’t know who they are, then how are we supposed to know?

Fortunately, the play has a center of gravity in Vera, the tart-tongued old communist in whose rent-controlled Greenwich Village apartment the play is set. The action begins as Leo, Vera’s wayward grandson, arrives at 3 a.m., having just completed a cross-country bike ride and been turned away from his erstwhile girlfriend’s apartment.

From the start, 4000 Miles is about miscommunication, grief and the effort required to bridge the distance between people that the title implies. Leo has trouble getting into the apartment because Vera has left her late husband’s name on the directory downstairs.

All is not well with Leo, who isn’t in school, and who has faced a string of misfortunes, including the death of his best friend. Played ably by Jackson Thompson, who has a long list of regional credits, including Sex With Strangers at Shaker Bridge, Leo comes off as a bit of a screw-up, or at least someone who’s struggling to get his head screwed on straight, as Vera might say.

Though they often argue, Vera provides Leo with a refuge, and Leo provides her with some companionship and help. Leo heads off to a climbing gym every day, a metaphor if ever there was one.

“It’s been a lousy couple of months for you, hasn’t it?” Vera tells Leo in the opening scene. Nowhere to go but up, it seems.

In the meantime, Vera, played with salty, steely verve by Peggy Cosgrave, last seen at Shaker Bridge in last year’s Other Desert Cities, is sinking slowly, losing her keys, her checkbook, her words and her friends. While she and Leo bond over family concerns and progressive politics, their generational differences push them apart.

As Leo’s girlfriend, Bec, White River Junction actor Irene Green plays a young woman still unsteady on her feet, older than her college classmates but determined to stay in school.

This is very much a character-driven play, and for it to work we have to care about the characters and their fates, such as they are. It’s no fault of director Susan Haefner that while the characters of 4000 Miles are facing real struggles, they are doing so in what feels like a cosseted atmosphere. The stakes are unclear. If Leo is struggling to find some purpose in his life, well, will he? Though the play is less a drama than a comedy, it isn’t often laugh-out-loud funny. A scene in which Vera and Leo smoke pot together is amusing, but that’s a low-hanging bud.

Part of what makes 4000 Miles a difficult proposition is that it is a document of its time and place, when urban progressives were embroiled in arguments across the generations over whose feminism was more powerful and affirming, never imagining that a crude internet troll would someday be addressing a joint session of Congress to affirm how brilliantly the first month of his presidency has gone. The divide on the left that this play dramatizes seems awfully quaint.

The ponderousness of the play’s ideological burden is briefly sloughed off thanks to the arrival of Amanda, a potential one-night-stand for Leo. She’s of Chinese descent, a sexy, self-directed future “international art star,” sure of herself in a way Leo, Bec and even Vera are not. Leo’s casual reference to Vera’s communisim shows how bloodless his political stance is as Amanda reminds him what communism means in China. New York actor Maya Naff, who like Irene Green is making her Shaker Bridge debut, plays Amanda with brassy charm.

In Enfield, at least, 4000 Miles has earned a subtitle: “The Play With All the Swearing That Upset the Town Librarian.” Seeing the show, I think the librarian has a point. Would even a callow 21-year-old man ever use the f-word in the course of shouting at his grandmother? The play is set more or less in the moment of its writing, so who knows what standards of decency obtain, but Leo’s impatience with his grandmother makes him hard to root for. Maybe we really are this coarse now, but that alone doesn’t justify the volume of foul language in a play about ordinary people trying to find their way in the world.

Vera is the play’s fulcrum, since she knows what the youngsters don’t — that life goes on, that this, too, shall pass. By the end, Leo has learned something, but Vera’s knowledge of who she is gives her a power the other characters lack, even as she feels herself faltering. She might be frail, but her wisdom and perseverance carry the play along and make it worth seeing.

4000 Miles, by Amy Herzog, is in production at Shaker Bridge Theatre in Enfield’s Whitney Hall through March 12. After Sunday’s performance, the cast will be joined by Lori Fortini, program leader of the Dartmouth-Hitchcock Aging Resource Center, for a talk about the play and about aging. For tickets and more information go to shakerbridgetheatre.org or call 603-448-3750.

Alex Hanson can be reached at ahanson@vnews.com or 603-727-3207.

Alex Hanson has been a writer and editor at Valley News since 1999.