My grandfather was 20 years older than my grandmother, and they remained married until he died at age 86, she being 66 at the time, and having been married about 45 years at that time.
Two sons, to this couple.
I have several friends where fairly big differences take place regarding age, and the marriages last.
Rush killed that argument with wife #1! Then buried it with wife #2. Then entombed it with wife #3! Rush is just the opposite of your grandfather and grandmother.
Had your grandfather already struck out three times prior to meeting your grandmother? Probably not. I’m sure they were lovely people and I doubt your grandmother married him because of his money, like so many younger women with older men these days.