Excel stores dates (and times) as days and fractional days -- the Windows default uses 19000101 00:01 (or maybe 00:00) as the start day-time. On MAC it's 19040101. At least one other spreadsheet uses 18991230 (Correct: Dec 30 -- why? I have no idea).

The value you report looks like a reasonable conversion from '02/09/2010' ("reasonable" or "close to" - didn't check for exactitude, but 110yrs *365 days/year = 41,150).

Depending on the precision of your needs you could simply divide the number you're getting by ( 365.25 * years ) -- but will be very rough. For greater precision, you can use a date module to do the conversion reliably.