To determine the percentage of all Americans younger than 65 years old based on the pie chart data:
- The age group 0 to 14 years represents 18%.
- The age group 15 to 64 years represents 65%.
To find the total percentage of Americans younger than 65 years, we can add these two percentages together:
18% (0 to 14 years) + 65% (15 to 64 years) = 83%.
Therefore, the percentage of all Americans who are younger than 65 years old is 83%.