So, on the fly, I can see that the first name is Alois, the DOB is probably 2 September 192... The word you read as Fähnlein is Jungbann, Garry. But I couldn't have interpreted it for sure either, but everything else fits perfectly. I was sure the following was the Bann number. So we have: 516, St. Pölten/Niederösterreich/Lower Austria. On the next line we find: Hermannschacht, Ober-Buhr.? That doesn't really make sense. At the bottom is the house number, 83, and Hermannschacht again. In villages it was common not to have a street name because there was only one anyway.
The postmark also helps us a bit, although it is unfortunately a bit thin: Öberwölbl...; and there is only Oberwölbling near St. Pölten, about 10 kilometres north of the city. And that's also where the village Hermannschacht can be found right next door.
As to the dating: I think the postmark says: 14.10.(19)4.... Unfortunately, I cannot decipher the last digit of the year.