Otherwise, this is a fascinating book, and it is among many accounts of war which should be read in high schools.
The site that oh8eleven links to states that Sajer was 16 when he volunteered to join the Wehrmacht in July of 1942; no DOB is provided in that article. (The article is discussing a debate about the veracity of Sajer's work.)
I couldn't take a side on this if I wanted to; this is the first time I am hearing that the book has been called into question.
Interestingly, Sajer died just a couple of days before his birthday last month.
("Sajer" was his mother's maiden name which he adopted for use during his military service, as his mother was German and it fit better with the names of the Germans he served with; his family name was "Mouminoux".)