A propos Dennis' promise to say more about the historian of mathematics, Dirk Struik, here's my favorite Dirk Struik (September 30, 1894 – October 21, 2000) anecdote: I have long been interested in Struik -- a life-long Marxist who ran afoul of McCarthyism while at MIT --, who taught at my very bourgeois high school, Vossius Gymnasium, in Amsterdam during the 1920s or so. Just before I was about to enter graduate school I was hanging around my alma mater (Tufts) when I heard from Jody Azzouni that Struik was about to give a lecture. It must have been during the Spring of 1995. Now, I was in the phase of my life in which I thought that Kuhn had to be historicized in all respects and I had just read Struik's brilliant Yankee Science in the Making (see here for an interesting appreciation), which dates from 1948. My immediate response was, "he must be over 100 years old!" Of course, I was told he was 100.
It was a great talk. A report of that lecture survives:
Well into his 90s [Struik] visited Tufts regularly, giving guest lectures in Lenore Feigenbaum's course on the history of mathematics at least every other year. Tufts faculty and alumni remember him, at well over 100, standing in front of the blackboard facing the audience and producing, without notes, a sweeping account of 19th century mathematics, providing literature references from memory as needed.
During the lecture I was seated not far from the eminent historian of science, I.Bernard Cohen himself over 80 years old at the time. During the festive intermission, Cohen leaned over to the person sitting next to him and said loud enough for a few of us to hear that Struik "had improved as a lecturer since he had turned 80."
There is hope for all of us.