List all the pay rates of all employees that were hired at 20 years of age.
pay rate refers to Rate; 20 years old at the time of being hired refers to SUBTRACT(year(HireDate)), (year(BirthDate))) = 20;
SELECT T2.Rate FROM Employee AS T1 INNER JOIN EmployeePayHistory AS T2 ON T1.BusinessEntityID = T2.BusinessEntityID WHERE STRFTIME('%Y', T1.HireDate) - STRFTIME('%Y', T1.BirthDate) = 20