If by “AA” you mean all accounts separate, the best recent U.S. estimate I found is that 51% of Gen Z couples (ages 18–29) keep their finances completely separate. Another survey found 38% of American couples completely combine finances, which implies 62% keep at least some money separate.
For younger married couples specifically, the Census found that among women who married at ages 20–24, 47% held all bank accounts jointly; among those who married at 30–34, the share was 29%.