From what I could find your gun is made by Winchester. It should say it on your gun somewhere though.
Sold by Sears Roebuck. Probably manufactured by Stevens.
If it is side-by-side, probably Stevens.
Yes.
50-150 USD
50-150 USD or so
No
"Your" Winchester Model 21 Double Barrel Shotgun was manufactured in 1933, giving it an age of 77 years, as of 2010.
1966 to 1988
Hunter Arms Company, Fulton, New York
The Ranger 410 double barrel was made for Sears Roebuck by Hunter Arms and by Steven Arms. Yours was Made by Stevens Arms.
Most likely Stevens they did make a model #5100
Made for Sears Roebuck by Stevens. There may be a model number on the right side of the receiver (most likely 5000, 5100, or 311) or a Sears product number on the barrel (101.6?) which could give an approximate date.