How can you tell the age of a gun?

The old joke is to saw it in half- and count the rings- but there is no one way to tell the age. It will depend on the make and model. In many cases, knowing the make and model and serial number, we can access published information. Some companies, such as Ruger and Browning, have it on their websites. Some guns, such as Remington, used a letter code to tell the date. In others, we can only tell the range of years that model was made. And with some guns, we can't tell at all, because we cannot confirm a maker.