How to calculate Age using Calculated Value of a Column

Created a calculated column called "Today Date", but this column will not be displayed in any of the views..
the formula is as follow:
=DATE(YEAR(Modified), MONTH(Modified),DAY(Modified)
initially i thought that this formula would auto-update today's date and store it inside this column, but i was wrong *ah wells*

next, i have a calculated column called "Their Age" and "Their Birthday"
the formula is as follow:
=DATEDIF([Their Birthday],Today Date,"y")
although it does return a age, it uses the date difference of "The date when u entered the value" and "Their date of birth"



try this formula:
   =FLOOR(DATEDIF(DOB,Modified,"d")/365,1)

hopefully it works :x