From Muppet Wiki

Younger versions of Statler and Waldorf were seen in The Muppet Christmas Carol (as young Jacob and Robert Marley) and in a cameo role in Kermit's Swamp Years. Younger versions of Statler and Waldorf also appeared in black and white in an "old" silent film in Statler and Waldorf: From the Balcony Episode 21 and in a '70's style in Episode 31.

Kermit's Swamp Years

Statler and Waldorf: From the Balcony

Statler and Waldorf: From the Balcony