As seen in the 1987 series episode Once Upon a Time Machine, an aged Leonardo exists in a possible future in which the Ninja Turtles have wiped out crime and ushered in a golden age of peace. He lives in a mansion with the other three Turtles, having retired from crimefighting. When news of Shredder's return arises, he leads the other Turtles to defeat him again.
He has become easily confused and forgetful with age, with the younger Leonardo referring to him as a "befuddled old coot."
With the help of the young Ninja Turtles and Hokum Hare from the past, both groups defeated Shredder, Bebop, Rocksteady and Bebop and Rocksteady's Gang.