The definition Khan Academy gave is "A statistical question is one that can be answered by collecting data and where there will be variability in that data. For example, there will likely be variability in the data collected to answer the question, "How much do the animals at Fancy Farm weigh?" but not to answer, "What color hat is Sara wearing?".
A-C all don't have variability. They are set in place. However, the ages of all people in your class can change annd thus exhibit variability.
