Basicly... your entire life.
I personally think there no specific age as long as your good at tennis and you win tournaments you can work your way up.
As the answer would take too long for this website, it is best to refer to the WilsonRacquet.net* link, below, which gives advice on how to become a professional tennis player. * (n.b., WilsonRacquet.net is not affiliated with the Wilson Sporting Goods company)
Ma Long from China
5 to 7 years
lol, that's funny question. the only answer for that is is "train train train"!
About 2 to 3 years.
The course lasts for one year .
For a few years.
9 yrs my dads one