In Stanton v. Stanton, the U.S Supreme Court ruled that Utah's statutory scheme which defined adulthood as 21 for males and 18 for females was unconstitutional due to gender discrimination. The case arose when a father stopped paying child support for his daughter once she turned 18, while continuing payments for his son until he reached age 21. The mother sued on behalf of her daughter arguing this violated equal protection under the Fourteenth Amendment. The court agreed with her argument stating that there is no rational basis in distinguishing between men and women at these ages since both are equally capable of managing their affairs upon reaching majority age.

In the dissenting opinion for Stanton v. Stanton, Justice William Rehnquist disagreed with the majority's decision to strike down Utah's law that set different ages of majority for men and women (21 for males and 18 for females) as unconstitutional under the Equal Protection Clause of Fourteenth Amendment. He argued that there was a rational basis behind this distinction made by state legislature - it reflected societal norms at that time which considered women mature earlier than men both physically and emotionally. Therefore, he believed such classification did not violate equal protection rights but rather served a legitimate state interest in recognizing these differences between genders. Furthermore, he expressed concern over judicial activism shown by court’s willingness to override legislative decisions based on its own interpretation of gender equality.