If you have the original box with the UPC symbol on the outside, below the SKU is a 4 digit production code. First digit represents year of manufacture, last 3 digits indicate the day of the year.
e.g. "9243" on my pistol indicates 2009, August 31 production date, which matches the test fire casing date exactly.
If you don't have the box or UPC sticker, the test fire casing included with most pistols should have a date stamp on it. Short of that, you'll have to index by finding other people with a S/N around yours.
Hope that helps.
PS +1 for
Greg Cote to buy mags... great guy to work with!