How can you find the age of a Stevens shotgun marked Stevens?

A key determinant is how the company name is marked (Stevens, J. Stevens Arms, J. Stevens Arms and Tool, J. Stevens Arms Co). Then you can date its manufacture +/- 20 years. Looking at the barrels...

the value of a 1948 Stevens double barrel shotgun 16 gauge. Hammerless.

Try your local gunsmith, rummaging through the bins at a gun show to see if you can find a match, or e-gunparts.com.

You can get an approximate date from the way the company name is marked on the gun. J. Stevens and Company = 1864 to 1886. J. Stevens Arms and Tool Co = 1886 to 1916. J. Stevens Arms Co = 1920 to...

Probably turn of the century