The 100 was Pelikan’s first fountain pen, and was the first to use a differential piston system, patented by the Hungarian engineer, Theodor Kovacs (see this page for more details). This particular pen was probably made between 1932 and 1938 in Germany. It is identifiable as a model 100 based on the incline on the feeder, as shown below. (For information on identifying other models such as the 100N and the 400, see this page and this page).
The engraving around the cap top reads “Pelikan D.R.P. Pelikan D.R.P.” which stands for “Deutsches Reichspatent”
This pen is certainly not in mint condition. One of the three fins on the bottom side of the feeder is cracked (seen in the photo below), and there is a small crack in the bottom of the cap.
In addition, the ink window has darkened considerably over the years.
If you are servicing a Pelikan 100 and intend to remove the piston assembly, note that it is screwed into the barrel of the pen with a reverse thread. See this page for more information.