Today is a special day for a colleague. Happens every 365 days.
A good friend here is 1388534400 today. At least that's what JMP tells me when I put her birthday in one column and today's date in another and then calculate the difference.
You see, JMP stores dates as the number of seconds since midnight on January 1, 1904. So today's date, October 26, 2009, is 3339360000 as far as JMP is concerned.
Fortunately, JMP has a host of built-in functions to help deal with dates in this format. See the whole list in the Formula Editor under the Date Time category.
One very helpful class of these functions are the In XXX() functions where XXX is a time unit. These functions return the number of seconds in the time unit specified. For example, In Minutes(1) returns 60. That is, there are 60 seconds in 1 minute.
These functions come in handy for converting JMP's seconds-based dates to something more readable, like years. You do that by dividing a number of seconds by In Years(1):
To save my friend's dignity, I'll let you use that formula to figure out how old she is.