Dear Sir,
Just as I thought! Perhaps Friedrich Vollbracht was born in 1897 instead of ten years earlier. At the age of 43 in 1940,he would've have more pep and vigor piloting the Messerschmitt Bf-110 twin-engined fighter and shooting two enemy planes down with it. 53 was too old to fly as fighter pilot if Vollbracht was born in 1887. I think probably the gravestone is correct in mentioning the year of his birth and his death.
Sincerely,
Edward