I suspect this is from Brian Patten’s Where Are You Now Batman?
Where are you now, Batman? Now that Aunt Heriot has reported Robin missing?
And Superman’s fallen asleep in the sixpenny childhood seats?
Where are you now that Captain Marvel’s SHAZAM! Echoes round the auditorium,
The magician’s don’t hear it,
Must all be deaf … or dead …
The Purple Monster who came down from the Purple Planet disguised as a man
Is wandering aimlessly about the streets
With no way of getting back.
Sir Galahad’s been strangled by the Incredible Living Trees,
Zorro killed by his own sword.
Blackhawk has buried the last of his companions
And has now gone off to commit suicide in the disused Hangars of Innocence.
The Monster and the Ape still fight it out in a room
Where the walls are continually closing in;
Rocketman’s fuel tanks gave out over London.
Even Flash Gordon’s lost, he wanders among the stars
Weeping over the woman he loved
7 Universes ago.
My celluloid companions, it’s only a few years
Since I knew you. Something in us has faded.
Has the Terrible Fiend, That Ghastly Adversary,
Mr Old Age, Caught you in his deadly trap,
and come finally to polish you off,
His machinegun dripping with years … ?