Where does business logic fit in the Command Query Responsibility Segregation Pattern?

Suppose I have a method like this:

public int CalculateAge(DateTime birthDate) 

Is this a Command? Query? Or should it be separated and not included as either a command or query?

It fits the query interface (TOut Execute(TIn input), but it’s conceptually not a query, more of a mutator.

For a command we would need to set a variable in the command and expose it since typically commands don’t return anything so that the caller could access the result. So, I don’t see a good fit there.