You can calculate the number of days that it has been since you have been born by simply multiplying the number of days in a year by the number of days that you have been here and then adding any remaining days of the current year up to todays date. For example a 24 year old would multiple 24 (years living) by 365 (days in a year) which is 8760. Then the days of this remaining year up to today would be added. September 13, gives 273 days for an approx. total of 9033 days. For a more exact date, look into to previous years to find leap years where an extra day would be added to the month of February.