I have noticed that with some old sitcoms, actors who were playing husband and wife sometimes had a big age difference between them. For example, Carmen Silvera was nearly 20 years older than Gorden Kaye, and looked much older as well and I am surprised she was cast as Edith in 'Allo 'Allo! given the age difference between her and her screen husband.
Dandy Nichols in Till Death Us Do Part was around 20 years older than Warren Mitchell, while the actor playing Wally Batty in Last of The Summer Wine was over 20 years older than Kathy Staff.
Out of American sitcoms, I have read that in I Love Lucy, the actors playing the neighbours had a big age difference between them - William Frawley was over 20 years older than his screen wife Vivian Vance, who actually commented that he should have been playing her father due to the age difference!