Speaking of Glenn Miller, Chattanooga Choo Choo was featured in the movie Sun Valley Serenade in 1940 with The Modernaires, Paula Kelly, and Tex Beneke singing ( if you haven't seen Dorothy Dandridge and the Nicholas Brothers dance, you're in for a treat).
But thinking about how real singers could still sing much later in life, here they are in a mid-80s tv show. I think Tex sings even better. He's looser.
And then amazingly Tex is still kicking in 1996 at 92
And @bartell has already quit.