The only period source for Saxon officers birth data I know about is for recipients of the Saint Henry Order, which includes birthdate and place with the citations for their winning deed. Schumann was singularly under-decorated by Saxony, so no such luck. I have a number of other ways to sometimes get around that-- if the officer made General in WW2, or was listed in the 1935 "Wer Ist's?" or was an SS officer and so on, but Schumann seems to have slipped off into obscurity.
Bavarian regular officers show their birth YEAR in Rank Lists. Württemberg regular officers (AND Prussian regulars assigned temporarily in Wtbg units) show FULL birth dates AND places (!) in their kingdom's Militärhandbücher (NOT in the joint Prussian-Württemberg Rank Lists). ALL naval officers show full birthdate in their Honor Rank List.
Schumann was very definite about his units' designations. The Palestine FZ 28 was an "orphan," no officers, no guns, used as a replacement "pool" (though those "waters" cannot have been very deep with no more than 20 enlisted men available

), so perhaps simply a goof and there were TWO far apart platoons accidentally numbered the same thing. He doesn't specify any "nationality" on any of the Flakzüge, and I only know which ones were Bavarian (and their types of guns) from "Das Bayernbuch," which lists that information.