Someone at p38forum.com might have the data you need.
Walther arms Ulm/Donau, Germany
You will need to contact Walther to find out.
1931 to date
You will have to contact Walther for the exact date.
The PPK/s is a PP with a PPK slide.
The Walther PPK pistol was first released in 1931. During that time the Walther PPK pistol was popular amongst European police and civilians because it was reliable and concealable.
Made in 1939.
No published sn data for Interarms PPK
The Walther PPK pistol is manufactured by German small arms maker Carl Walther GmbH.
Impossible to answer without the serial number.
I believe you are asking about a Walther PPK/S made by Umarex. I would contact Umarex directly and ask them at Customer Service. See the link below.
You will have to contact Walther