From Automobile Magazine:
The 1960s saw two major trends unfold that would dramatically affect the new-car market, and the Ford Mustang was designed to capitalize on both. The first shift was the changing demographic landscape, with the leading edge of the baby boomers starting to reach driving age. In 1964, the 16-to-24-year-old age group was the fastest growing in America. Young people did not want to drive the kind of cars their parents drove. They wanted bucket seats, floor shifts, and the sporty feeling of being close to the road. (What a difference from young drivers today.) The second trend was the massive increase in two-car households. In 1959, only a million families had more than one car; by 1964, that number had skyrocketed to thirteen million.
Read more: http://www.automobilemag.com/features/news/1404-on-this-day-ford-mustang-debut/