What is the most suitable time for studying new language ?.

Hi everyone ! It's the first time I have logged in English forum. I wanna ask a question and hope to get good explanation. As I heard, scientists suggest that people should start to study the second language as soon as possible. Because in that time, brain is almost empty and able to digest any new guideline or data with maximum efficient. However, in the case of those who doesn't have basic foundation and they just focus on learning new language due to job requirement. They say that after few years or even less than, they can use fluently another one for all skills. Therefore, I' m little confused at this point. For example, I began studying English since I was a little boy, but I abort it for some years. When I entered university, I decided to get used to English again. I spend a lot of time for doing grammar, training my ears and practicing speaking. As a result, I get 80 points for Toefl Ibt test. However, I still find myself very hard to think and try to describe what I meant by English. Moreover, there is burden for me to catch up with song lyric or common communication on film with American or English accent. Can anyone tell me persuasive answer for my concern. Otherwise, please give me some hint for problem right now. I really deeply appreciate your help. Thank you !