Your Walther PPK should have a number stamped on the barrel cowling in the ejector port. Probably next to an antler, indicating the date it was proofed, and where (most were proofed in Ulm, hence the antler which is the code for Ulm). That would be the date of manufacture. If there isn't one, tell us the first few digits of the serial number and then ### the rest and I'll look it up.
Your pistol was made in the 60s or 70s when there was a West Germany. 50's guns were "Manurhin" / French marked, just over the border from Ulm. They're nice pistols, more than 90% of them were made in .32 / 7.65, the rest in .22 and 9mm K or .380. The .32 is accurate, pleasant to shoot, and, as long as you touch your thumb to your "driver greeting finger" when you grip the pistol, safe. If you have bigger or meaty hands, you should either learn how to hold it (thumb to which finger?) or not shoot it, since you'll get a very painful groove carved into the web of your hand.
I will dig out my books to see what postwar crown proof marks mean. Prewar, they all got Crown over N proof marks.
