Answer:
Age
Explanation:
Independent variable: In a psychological or scientific experiment, the term independent variable is defined as the variable that is being manipulated or controlled or changed during an experiment by the experimenter.
In an experiment, the experimenter changes or manipulates the independent variable to see its effects on the dependent variable, i.e, any changes in the independent variable will cause changes or alteration in the dependent variable.
In the question above, the independent variable is Age.