Evelyn and Christopher Wilcock
Many towns in Germany kept personal files on inhabitants which give the date of birth.
These files are not official certificates and in Frankfurt am Main were held in the Town Archive where researchers like myself were able to read them.
This means you do not need an official certificate which is closed until after a date limit. I have Kaufmanns on my own tree so did a search.
I have not found a record for your Kaufmann on the on line 1939 German Jewish census which (in theory) listed anyone Jewish or in a household that included anyone of Jewish descent
A presumably non Jewish Joachim Kaufmann is listed in the address book for the Nazi period
Residence Date: 1940
Residence Street Address: H 22 KaiserFried richStr 521.
Residence Place: Leipzig, Deutschland (Germany)
Title: Adressbuch d. Reichsmessestadt Leipzig