beretta 92fs

Question
How can I tell, or find information when my firearm was manufactured

Answer
The Beretta 92 was developed in 1972, but was not adopted by the US military until 1985 (Model M9), so your gun is certainly was not manufactured before 1985.

The only way I know of to get a precise date is to call Beretta with the serial number. Most gun companies will, for a small fee, research the gun by sn, authenticate it, tell you its date of mfg, and apprise you of anything interesting or peculiar about that particular gun.