Q. How is my age calculated? 

According to Revenue Ruling 2002-62 Section 2.02(a), when referring to the age column in the life expectancy tables: “The number that is used for a distribution year is the number shown from the table for the employee’s (or IRA owner’s) age on his or her birthday in that year.
If the joint and survivor table is being used, the age of the beneficiary on the beneficiary’s birthday in the year is also used.”