"Fishing Knife" AKA: Toothpick" or "Texas Toothpick" or "Rib Tickler".
The "Push to Release" tab lock used to be quite common.
It wasn't jusi the Imperial-Schrade companies that used it.
I
think that lock dates from the late 1890's or very early 1900's.
I
think the tang stamp is pre 1955. My
guess is sometime in the 1930's (maybe earlier. I'm not sure when they got the patent for shell construction) ... maybe post war 1940's.
it is "almost impossible" (personally, I think it
is) to get the exact year of manufacture on Imperial-Schrade knives, unless the pattern was only made for one year.
EDIT:
As
Boattale
mentioned, it has been sharpened quite a bit, The blade was originally longer, and had a bit of belly at the point.
It should still be useable, however.
Does the point stand proud of the handle when closed? If so you can lower the tip by SLIGHTLY filing the kick. (it don't take much; go slow and check often.)