help:

Use DateDiff with the "yyyy" interval type parameter to find the number of years difference between two dates. This use of DateDiff is the same as finding the difference between the year of endDateTime and the year of startDateTime.

DateDiff ("yyyy", #10/7/1999#, #2/10/2005#)

Returns 6.

DateDiff ("yyyy", #12/31/1999#, #1/1/2000#)

Returns 1 (a 1 year difference), even though there is only a 1 day difference between the dates.

DateDiff ("yyyy", #1/1/1999#, #12/31/1999#)

Returns 0 (a 0 year difference), even though there is a 364 day difference.

или

Use DateDiff with the "m" parameter to find the number of months difference between two dates.

DateDiff ("m", #3/15/1999#, #7/13/1999#)

Returns 4.

тогда результат делить на 12