I sincerelly think that learning comes with effort and need of something (a position, a promotion or fear of being cheated, misunderstood etc).

   The problem is; when we are grown ups we have the government taxes, the power to pay, and a varied assortment of bills (plus, the car demanding tires, oil inspections, breaks and all that...).

   A proof that an adult learn new tricks is, when he changes to nother job, other city or other boss.  He quickly adjust to the new situation.  Of course, there are a few exceptions that only confirm the rule.

   But, then, even children themselves have different paces in their learning.

  PP.