If you say that your best learning is before 20, either you are not doing it right or you are younger than 20… If you are learning right before you are 20, then you will, b Ezras Hashem , learn even better when you are older.
And if you are a smart learner, you can find a couple of hours a day to get yourself a job skill. And if you are not, then for sure you need to get a job skill and not plan to earn money from your learning