Hubert Zafke was rolled into the courtroom in a wheelchair, holding a wooden cane, by one of his sons for the trial, which had been postponed three times because of health concerns.
The charges focus on a one-month period in 1944 when 14 trains carrying prisoners - including the teenage diarist Anne Frank - arrived at Auschwitz-Birkenau.
Frank, who arrived in Auschwitz with her parents and sister, was later transferred to another camp, Bergen-Belsen, where she died in March 1945.
Prosecutors have charged Zafke was aware that the camp in Nazi-occupied Poland was an extermination camp, and have accused him of at least 3,681 counts of accessory to murder.
Some 1.1 million people, most of them European Jews, perished between 1940 and 1945 in Auschwitz before it was liberated by Soviet forces.
After prosecutors read their charges against Zafke on Monday, the trial in the northeastern city of Neubrandenburg was postponed again until next Monday.
Prosecutors had asked the chief judge to recuse himself because he had been unwilling to start the trial in the first case, citing Zafke's poor health, before being overruled by a higher court.
The question of whether Zafke is fit to stand trial was also due to be addressed again by the court next week.
More than 70 years after the trials of top Nazis began in Nuremberg, Germany is racing against time to prosecute the last Third Reich criminals.
Last year Oskar Gröning, dubbed the "Bookkeeper of Auschwitz", was sentenced to four years in jail as an accessory to murder in 300,000 cases in 1944.