Men and Women in those eras were breaking into the professional rankings way before they hit 20 years of age (much younger for the women). In today’s game, both the men’s and women’s average age in the top 100 world rankings has increased significantly.
There are many tennis professionals that have gone through the College/University system whom have played or are currently playing on the ATP and WTA tours. A few to mention; John Isner, Kevin Anderson, Bob & Mike Bryan, Lisa Raymond amongst others.
With the average age now being much older on tour, going through College/University is now the best option to develop your tennis game further.
With state of the art facilities, USA Colleges/Universities provide high quality training, coaching and competition to players and most importantly, an academic degree.
At the end of the degree course the graduate would then be only 22 years of age, with a degree in their choice of field and potentially, another few years at having a shot at turning professional.
You can see in the charts ‘experience matters!’