The last 5 presidents to die did so after 1960, when modern surgical techniques were well established, cardiovascular surgery was rapidly developing, there was a large antibiotic armamentarium, and many cardioactive and and vasoactive drugs were available. The median age of death of these 5 was 81. Each group consisted of one nonagenarian, two octogenarians, one septuagenarian, and one sexagenarian. The median age at death was 73.5 years. The second half of this group died between 1885 and 1994.
Presidents are remarkably immune to cancer death.
The figures don't speak very loudly to modern medicine as a prolonger of life, at least for famous old white men, but I think we have to give medicine its due in certain individual cases. Washington died at 67 of quinsy, and I think just about everybody would agree that such deaths are very uncommon in modern times. Possibly ENT surgery could have saved Grant, as it apparently did Cleveland, and colorectal surgey saved Hoover and Reagan. The medicine of the fifties possibly kept Eisenhower's Crohn's disease sufficiently at bay, whereas a similarly afflicted counterpart of the nineteenth century may not have remained hale enough to rise to such high position, likewise for Kennedy and his Addison's disease. In one of the interesting coincidences of American history, Thomas Jefferson and John Adams died within a few hours of each other on the 50th anniversary of the signing of the Declaration of Independence, July 4, 1826.