Stamped on the left side below the breech is 4691, indicating the year of manufacture as 1964, as I understand it. It has the typical wear and tear that you'd expect in a pellet gun owned by a couple of reasonably responsible teenagers and then stored in the closet for several decades. I doubt that it's had more than 250 pellets fired through it.
There's some rust in various places - trigger, trigger guard, sight, plate on the left side of the receiver, and the bolt head on the underside of the stock. There's some pitting in the surface of the metal between the two horns of the rocker style safety. The finish in several places on the barrel and air cylinder is worn. The stock appears to be walnut and has the original finish. There's one ding in the wood near the butt, less than 1/16" deep and about 5/61" long.
Other than that, there are some minor scratches that could be easily removed in a couple of minutes with steel wool. There are about a dozen tiny marks on the sides of the barrel behind the sight where my friend had mounted a scope.
The pump mechanism works and holds pressure. I don't have any means to measure the velocity, but it's impressive. The stock is in good shape and can be easily refinished to fine condition. There are no cracks or water damage. Let me know if you have questions or would like more photos.
There's most of a can of pellets around here somewhere. I'll include them if they turn up. The item "1964 Sheridan Blue Streak 5mm 20 Cal Pump Pellet Air Gun Rifle, no damage, works" is in sale since Thursday, March 4, 2021. This item is in the category "Sporting Goods\Outdoor Sports\Air Guns & Slingshots\Air Rifles".
The seller is "dwa1999" and is located in Ocean Springs, Mississippi. This item can be shipped to United States.