Why, then, did he claim that he was born two years later, in 1772? In his Heiligenstadt Testament of October 1802, he even implied that he was three to five years younger than his real age.
One explanation may be that his parents wanted to present him as a Wunderkind and that he believed them. The younger, the greater the Wunder. Another that the uncertainty about the birthday, or even the parentage itself, may be connected in some strange way with his chronic and seemingly inexplicable unwillingness to deny the rumour that he was the illegitimate son of a king of Prussia, either Friedrich Wilhelm II or Frederick the Great himself.
Again and again Beethoven’s nephew, Karl, and his friends asked him to refute the rumour, which first appeared in print in 1810 and which had gained wide currency in England, France and Italy and, of course, in Germany. He would not do it until he began to suffer from the illness that was to bring about his death three months later, on March 26, 1827. What took him so long?
“I have adopted the principle,” he wrote to his old friend Franz Wegeler on December 7, 1826, “of neither writing anything about myself nor of replying to anything that has been written about me. Hence, I leave it to you to make known to the world the integrity of my parents and especially of my mother.”
Everything has a reason, good or bad. It just so happens that we do not know what had blocked him.
Source: Beethoven, by Maynard Solomon