Such a rule did not hold in my time, at least not among the people I knew. The only women any of us ever saw were women that were dating our friends.If it were not permissible to date them in our turn, we would have had no one to date.
Instead, it was a "competitive game," a way for girls and boys to demonstrate their popularity.
With the rise of the entertainment culture, with its movie houses and dance halls and their universal appeal across class lines, dating quickly moved up the socio-economic ladder to include middle- and upper-class men and women, as well as the new urbanites.
When one tries to understand how dating has changed over time, and most importantly, how we arrived at the system of courtship and dating we have today, one must realize the monumental cultural shift that occurred during the 1940s, primarily due to World War II.
These people will have dates on a regular basis, and they may or may not be having sexual relations.
This period of courtship is sometimes seen as a precursor to engagement or marriage.