Is it too late to take the college entrance examination at the age of 20?
Unrealistic, because you have forgotten how to learn the basic knowledge in books, which requires you to start over and waste a lot of energy. I suggest you start planning your own path and then specialize in a knowledge you love. I believe that in the near future, you will become an elite who has never learned much but is busy with your career through your own talent and yourself. In any case, it is most important to choose a path that suits you.