Marjorie Rhodes was, in fact, 69 when the film came out in 1966, having been born in 1897. However there is probably a very good reason for her taking the part of Mrs. Fitton in the film - the film was an adaptation of the play "All in Good Time", and Marjorie Rhodes had that part in the play. More than that, she played it on Broadway, and was nominated for a "Tony" award in 1965 so that was probably in her favour.
Yes, there is an age gap, but in view of the superb performance I'm sure it could be forgiven, if not overlooked!!
Marjorie Rhodes was so heartbreakingly poignant in the role of the mother that I never thought about an age gap at all, besides, if you have seen what working class life did to the faces of women up to and including the sixties, take a look at Coronation Street or any one of a number of kitchen-sink dramas of the period, and you will see how life prematurely aged them ... some women in their forties looked closer to seventy.
But you ARE Blanche ... and I AM.