By it's serial number.Go to proofhouse.com to find the date of manufacture.
If you provide the serial number in your question then I can give you the date of manufacture.
If it has the 17 digit vin, the 10th digit is the code date of manufacture.
If you would post the serial number and model number,I can give you a date of manufacture.
serial #
You have to call SIG to find out.
You will have to call Beretta
Use the link to date this Browning
Walther uses a date code of two letters.
You will have to call S&W to find out.
You will have to call Colt with the sn to find out.
Contact Browning.