Early studies of adult intelligence led researchers to the ...

[savannahhooper]

Early studies of adult intelligence led researchers to the conclusion that intelligence in adulthood
 
  is plastic and variable, and may either increase or decrease.
  increases slowly during the 20s and early 30s, and declines thereafter.
  peaks at about age 18, remains stable until the mid-20s, and declines
  thereafter.
  is most significantly affected by experience, such as war traumas.

Question 2

The term g refers to
 
  grand intelligence.
  general intelligence.
  great intelligence.
  gross intelligence.

[Danny Ewald]

Answer to Question 1

peaks at about age 18, remains stable until the mid-20s, and declines
thereafter.

Answer to Question 2

general intelligence.