Jim Kweskin and Geoff Muldaur at the Lobero Theatre

Two songs into their too-brief set, Jim Kweskin quipped, “Geoff [Muldaur] likes to say we play for old people … and their parents.” Looking around at a theater full of beaming boomers, we all laughed along with the joke. Still, after some beautifully played, low-key, and tastefully constructed songs, just as the evening seemed ready to move into more blissful explorations, it all suddenly ended. These old folks were calling it a night after barely an hour of strumming and fretting.

If that seems cruel, it’s also a testament to why older people gather at these functions. It’s here that they can calmly remember the exuberance of their own youth, a time when people like Kweskin (and Dylan and Garcia) first employed old-timey tunes, blues, and the country swing of folk music to revitalize the processed pop of the early 1960s. Younger people can’t be expected to “get” this nostalgia for nostalgia and have a right to expect more immediate energy onstage. Make no mistake: Good stuff was there on Saturday, from Kweskin’s heartfelt signature reading of “Blues in the Bottle” to Muldaur’s beautifully grained “Fishing Blues” and revelatory “Down on Penny’s Farm.” What was onstage was fine; it just seemed over before it was done. They played only two more songs than the openers.

And that job fell to homies: Tom Ball and Kenny Sultan (and brilliant cardboard-wine-box drummer Jody Eulitz), who delivered a breezy set. They also gave us the evening’s only ice-blue surprise: an unlikely guitar solo discovered by Lawrence Welk in 1930s Cuba, touchingly strummed by Ball, who usually plays harmonica. It was reinvigorating — you know, like American roots music used to be.