32 year age difference between Cary and Joan

There was a 32 year difference between Cary Grant and Joan O'Brien who were paired off in this film, and Dina Merrill was 2 years older than Tony Curtis and yet she played his love interest.Cary was 55 when he made this film and Joan was 23 years old.Tony Curtis was 34 when he made this ,and Dina was 36 yrs old.It would have made more sense(IMO) to pair off Dina and Cary, and Tony with Joan.The age differences would then be 19 for Cary and Dina, and 11yrs for Tony and Joan.It's just numbers, the movie is still enjoyable,although making fun of war is a contradiction.The age differences between male and female leads has always been a Hollywood conundrum and at least Cary was classy enough to recognize it.