Although it is tempting to attribute bigoted views to age, that tends to be the case because the elderly grew up in a different world and have maintained the views of their youth, and the newer generations have become more accepting- but this is more related to the twentieth century.

Although it is certainly possible that Martin Luther just decided that he hated the Jews as he got older (and part of that might be related to a perceived lack of success in converting the Jews to his form of Christianity relative to Catholics) I believe it is far more likely to have been a political move on Luther's part.

John Frederick of Saxony, one of Luther's chief supporters and protectors, did not allow Judaism in his realm. He may have been asked (or coerced) by John Frederick to incorporate anti-Semitism into his religious system.

In a very similar vein, there had been a proto-Protestant revolt in Germany almost two decades before Luther published 'On the Jews and their Lies'. This Peasant Revolt of 1524-1526 consisted primarily of unhappy commoners who considered themselves adherents to Luther's teachings. The idea of a personal god can be a powerful drug. Yet, Luther sided with the German princes and fully condemned the revolt in 'Against the Murderous, Thieving Hordes of Peasants.' I find it even less likely that Luther hated the peasants than the Jews. Luther was not a member of the nobility (although he was the son of a wealthy town notable) but throughout his career depended on nobles to protect him, without whom he undoubtedly would have ended his life at the stake.

Luther's vitriol against the peasants and Jews was much more about self-preservation (and the preservation of his movement) than it was motivated by actual hatred.