@Catherine - You didn't expose your age in your OP. If you had, I wouldn't be asking how old you are. How is it relevant, you may wonder. Well, I think if you are a teenager your chances of becoming a really good English speaker and using it for your profession before the age of 40 are much better than if you are 39. 

aegis, I guess if you ever paid your attention on my subject, you should already get the answer. Though I didn't mean to expose my age.

It's never too late to do something!

It depends on the market.

This is because for becomming professinal, you need to get money by someone else.

If the demand level market requrire is not so high, you can easily become professional.

If the level is too high , possibly you cannot become.

The point is , you cannot decide to become professional by yourself.

(Even if you open English school by yourself, if you cannot get any student, you cannot become professional.)

The other day, someone also told me about Jack Ma, what a coincidence! haha