Many of my students ask me, "How much should I play?" Usually, juniors tend to over train. This causes injuries and "burn out." I feel it is better for a student to learn to focus and practice positive point play than to worry about how many hours they are playing. Juniors tend to practice too much and lack match (mental) plans and adults tend to play matches all the time and lack the practice time.
The actual chances of a player making it professional as a tennis player are slim. I would much rather see a player play tennis, handle his schoolwork, learn social skills and have fun outside of tennis. I find this is more healthful and constructive. We need better-adjusted adults. Put your tennis in perspective. As you become older, the social contact you make through tennis become increasingly important.
Many juniors that I have taught were so focused on becoming great when they were starting, that when they did not reach their goal, they quit. Now, I have more and more students coming back to me saying, "I did not play in college, but I started playing tennis again. Now, it is so much fun and all the things I learned earlier are coming right back." Remember that tennis is a sport for a lifetime.
Have fun on the court!