According to information contained in a book titled L.C. Smith Shotguns by Lt. Col. William Brophy, USAR Ret., your 20 Ga. hammerless, ejector gun, Serial No. 5549, was manufactured in 1909, and was part of a production run that included serial numbers 5,380 through 5,677.
My guess is that yours is a No. 00 Gun, introduced in 1898 and produced through 1912. The 20 Ga. version was introduced in 1908, and was available equipped with optional automatic ejectors as well as the Hunter One-Triger. A key to identification as a No. 00 gun will be marking on the barrel(s) reading "Armour Steel."
Hope this helps.
Good luck, and good shooting!