Dealinng with Dates in javascript is a pain .....there are some nice functions in FormCalc that allow you to do this and cange formats quickly.
To do date arithmentic you will have to use Date2Num (a FormCalc function) that will give you the number if days from a set point (called an epoch). If you change both values into a number, then you can subtract them and get a number of days. You can then manipulate that number to give you years or whatever you would like.
If you post your email address I can send you a couple of date arithemtic samples that will give you the general idea.
