why age makes little difference in vocabulary building?

    I repeat ,no matter what your present age.
   You may be laboring under a delusion common to many older people.
   You may think that after you pass your twenties you rapidly and inevitably lose your ability to learn.
   This is simply not true.
   There is no doubt that the years up to eighteen or twenty are the best period for learning.Your own experience no doubt bears that out.And of course for most people more learning goes on faster up to the age of eighteen or twenty than ever after.even if they live to be older than Methuselah.(That is why vocabulary increases so rapidly for the frist twenty years of life and comparatively at a snail’s pace thereafter)
   But (and follow me closely)
   The fact that most learning is accomplished before the age of twenty does not mean that very little learning can be achieved beyond that age.
   What is done by most people and what can be done under proper guidance and motivation are two very,very different things–as scientific experiments have conclusively shown.
   Furthermore–
   The fact that your learning ability may be best up to age twenty does not mean that it is absolutely useless as soon as your twentieth birthday is passed.
Quite the contrary.
   Edward Thorndike,the famous educational psychologist,found in experiments with people of all ages that although the learning curve rises spectacularly up to twenty,it remains steady for at least another five years,after that,ability to learn(according to Professor Thorndike) drops very,very slowly up to the age of thirty-five,and drops a bit more but still slowly beyond that age .
   And
   Right up to senility the total decrease in learning ability after age twenty is never more than 15 percent!
   That does not sound,i submit,as if no one can ever learn anything new after the age of twenty.
   Believe me,the old saw that claims you cannot teach an old dog new tricks is a baseless,if popular,superstition.
   So i repeat:no matter what your age,you can go on learning efficiently,or start learning once again if perhaps you have stopped.
   You can be thirty ,or forty,or fifty,or sixty,or seventy–or older.
   No matter what your age,you can once again increase your vocabulary at a prodigious rate-providing you recapture the “powerful urge to learn” that is key to vocabulary improvement.
   Not the urge to learn “words”–words are only symbol of ideas.
   But the urge to learn facts,theories,concepts,information,knowledge,understanding–call it what you will.
   Words are the symbol of knowledge,the keys to accurate thinking.Is it any wonder then that the most successful and intelligent people in this conuntry have the biggest vocabularies?
  It was not their large vocabularies that made these people sucessful and intelligent,but their knowledge.
  Knowledge,however,is gained largely through words.
  In the process of increasing their knowledge,these successful people increased their vocabularies.
  Just as children increase their vocabulary at a tremendous,phenomenal rate during those years when their knowledge is increasing most repidly.
  Knowledge is chiefly in the form of words,and from now on,in this book,you will be thinking about ,and thinking with,new words and new ideas.

[new words]
tremendous 巨大
prodigious 惊人的
senility 衰老