Back in high school I played 3-4 hours a day and about 7 hours on Sundays. I felt fine at the end of the day but mentally I was a wreck on the court. I was invinsible back then, injuries, what are those? An ache or pain went away WHILE I played tennis and never came back. Now, at age 31 an ache stays for months if not years. Scary stuff. I am still very much in shape and can still play a ton, but my lingering injuries only let me play so much. Just you wait. When I was your age I said it would never happen to me, I was a machine. pfft, what did I know?
At first I thought you said you were in invisisble. That would be a fantastic advantage on court!!!!
I guess you ment invincible, which is how I felt back in college and was playing for 3 hours then practiced with the team for a couple, then played around another hour or so until we went to Taco Bell for our dinner.
Stretching??? What's that?
Now I am paying big time for never getting a proper answer for that question. Or maybe not listening to it when I did get an answer.
There have been a few scattered pros who started in their teens. There has been 1 or 2 that started at 20 or 21. But the vast majority started at 7 or 8. Agassi was video taped hitting with Jimmy Conners at the age of 4. Conners was quoted as saying if this kid beats me I'll retire. Agassi beat him at the US Open in '88 (I think).
So where does this get you? It tells you that you can be a pro starting at age 13. But I would say it takes heavy doses of;
hand eye coordination;
athletism & balance;
the drive to get what you want;
love for tennis (because you will have to live and breath it for 5 years or more)
You will have to skip a lot of the fun that kids have. Social gatherings, and holidays will have to be put aside for practice and tournaments.
All for the dream of being a tennis pro with the understanding that a very small percentage of players achieve that dream, no matter how hard they work and sacrifice.
If I were to give you one piece of advice (other than what I've already written here) it would be to have a back up plan. A plan B. I would work hard to be the best tennis player I can be with one eye towards a professional career, and another towards a college scholarhship. One is a dream that may come true with a lot of luck and the other is something you can use for the rest of your life.