The 75yr old woman on average has much less income because:
She was born in 1937
At 8 years of age she was subjected to the government campaign to ensure jobs were available to the returning troops.
As Elvis Presley and Pat Boone were topping the charts she graduated high school where she might become a Nurse or Teacher if she was really lucky and talented. But even then she was expected to find a good husband and become a housewife and mother. What jobs she might have held during her youth all had the posted "Men's Wage Scale" and the "Women's wage scale" hurting not only her income but self esteem as well. When Sputnik flew overhead and captured the imaginations and fears of young men across the country. She was being pressured that to support her husbands self esteem a good wife would never work outside the home. By the time feminism came about in the 60's she was more worried about caring for elementary school age kids.
So today she settles for the greater of her personal social security or 50% of her husbands social security and whatever survivor benefits she may be entitled to from his pension. It's lower on average than the typical man born the same year because of 75 years of sexism. And the only true fix for that is to roll back the clock and create total equality from 1937 forward. But I don't know how to do that.
On edit the above is nothing members of this board are not aware of. My point is that by fixing the discrimination at day 1 of life the problems 75 years later will have fixed themselves. We can work the human problem of meeting our elderly needs. But there is little to be gained by focusing on the gender aspects as their current situation is more a function of what has already happened as opposed to what is currently happening. What we can control is the messages that 8 year old girl receives about her worth and place in society. By fixing what would otherwise be a lifetime of repression. We solve the issue of her retirement years. Something I can't do for the woman born in 1937. But can help that 75 year old woman in 2079.