The 77-year-old singer-songwriter David Crosby’s argument that performing keeps musicians youthful certainly applies to Frankie Valli. The legendary New Jersey singer is 84, yet pulls off a two-hour show with more than two dozen songs, many of them standards, delivering a joyous celebration of pop music at its sweetest and purest. Valli doesn’t need new material when his catalogue of smashes ranges from the doo-wop days to the disco era and – with the original Four Seasons long disbanded – a new, youthful band and harmony singers can render them to perfection. The hit Four Seasons musical Jersey Boys has given him a much younger audience, who respond to hits such as Rag Doll, Walk Like a Man, Sherry, Let’s Hang On and the rest with rapturous chants of, “There’s only one Frankie Valli.”

This is so true. His piercing falsetto is one of the most extraordinary sounds in pop, and its power belies the decades. Valli is mortal, though. He’s less nimble on his feet nowadays and this is a farewell tour, but the black-suited singer who was born Francesco Castelluccio still radiates Italian-American cool – there’s something of Al Pacino about him – and bone-dry wit. “We’re gonna slow things down a little,” he says. “Because I need to.” A sublime Silence Is Golden is drily dedicated to “all the politicians in the world”.

Meanwhile, the stellar setlist gives a lot, then gives some more. Beggin’ and The Night are top-drawer northern soul. Valli throws John Travolta dance shapes for the theme from 1978 movie Grease. By the time he gets to My Eyes Adored You, December, 1963 (Oh, What a Night), I Love You Baby and Bye, Bye, Baby, the house has been brought down so many times it may need new foundations. He seems emotional as he thanks the audience for his career and admits that crowd reactions are already making him reconsider retirement. With such waves of joy offstage and on, you can see why he doesn’t want to stop.

• At SSE Hydro, Glasgow, 29 November. Then touring.