Looks like a 1934 vintage:
http://www.tague.at/pistolen/en_index.htm
Click on "Walther PP, PPK Table with Year of production"
For more, try starting here:
http://www.waltherforums.com/forum/faq-pp-tp/10152-some-websites-help-pp-ppk-owners-id-their-guns.html
Original caliber, 1st...