"The gods who nurse this universe think little of mortals' cares. They sit in crowds on exclusive clouds and laugh at our love affairs. I might have had a real romance if they'd given me a chance. I loved him, but he didn't love me. I wanted him, but he didn't want me. Then the gods had a spree and indulged in another whim. Now he loves me, but I don't love him." - Cole Porter
Ok can we all think about this logically for a moment?
Sally and Phyllis both are 20 years old in 1940...making them at least 50 YEARS OLD in 1970 which is when Sondheim set the original show.
Even if this is making the transition from stage to film, ages and time spans should stay the same. If Sorkin sets the movie in the present and keeps the women young in 1940, that would technically make them almost 80 YEARS OLD.