Maybe you won’t share my reaction, but my first surprise at this week’s preview of Clint Eastwood’s Jersey Boys came even before the movie started: The age of many in the audience. Perhaps forty percent of them were thirty or under, a lot of them considerably under. This suggests that the music of Frankie Valli and the Four Seasons is more deeply and widely ingrained in popular consciousness than I anticipated, despite dating from an era considerably before these youngsters were born.

And another cross-generational element is supplied by the 84-year-old director. Jersey Boys is a zingy, large-spirited, fast-moving movie, and I don’t think it’s patronizing to note that it has a youthful vibe. It’s also Eastwood’s best effort since his twin Iwo Jima movies eight years ago: it resembles virtually nothing else he’s ever done.

Adapted from the extremely successful musical play (still playing in New York after almost nine years), and scripted by the play’s authors, Marshall Brickman and Rick Elice, the movie bears only one obvious sign of its stage origins: Three of the four main characters—Tommy DeVito (Vincent Piazza), Bob Gaudio (Erich Bergen, reprising his role from the play’s national tour) and Nick Massi (Michael Lomenda, also from the tour) intermittently take turns addressing the audience to give their individual spins on the group’s rise and fall. As used here, the device works, fitting into the movie’s breezy, frequently comedic tone.

The picture’s portrayal of the quartet’s hardscrabble Belleville, New Jersey beginnings, for three of them, including Valli (John Lloyd Young, star of the Broadway show), and its uncertain ascent to phenomenal success in the 1960s is so genially and comically written and directed, that when things take a soapy downturn in the last third, the transition is a little rough. But Jersey Boys never loses its momentum for long.

This version of The Four Seasons’ story mostly follows Valli’s career and personal trajectory and favors him in crucial matters. Young’s performance is much more than adequately proficient, but the movie makes his Valli a gifted but somewhat passive character to whom things happen. These things are usually produced by the mutually antagonistic Gaudio, the composer of the group’s signature songs (“Sherry,” “Walk Like a Man,” etc.) and DeVito, a small-time hustler and hood, and a gopher for gangster Gyp DeCarlo (Christopher Walken), a kind of fairy godfather to Valli and company.

How much of all this is accurate may be an open question, but it carries you along with its vividly broad-brushed style. (Although, a little curiously, Tom Stern’s photography goes for a muted, often sepia-toned palette.)

There are, of course, the songs, the raison d’être for everything else, recreated meticulously but excitingly by the four actors, particularly in Young’s almost uncanny impression of Valli’s singing.

Jersey Boys has flair, pace and rough-edged wit, and just enough old-fashioned show business heart.

Opens Friday at Flix, Maple Ridge, Regal Elmwood, Regal Niagara Falls, Regal Quaker, Regal Transit, Regal Walden Galleria, Sunset Drive-In

Watch the trailer for Jersey Boys