We have better living today due to drugs and understanding the germ theory that was just beginning to be accepted as fact when Lee died.
The Lee in that picture had already suffered from:
- severe mental strain during the Mexican War (PTSD?)
- A bloody wound at Chapultepec
-Malaria
- A severe summer cold (first two months of his command of the ANV)
-Fall from his horse that sprained one hand and broke several bones in the other (his arm was in a sling at Antietam)
-A second major cold in the spring of 1863 that some say was a symptom of his heart problems that began that year with sharp pains in his chest, back and arms.
-At Gettysburg he had severe diarrhea and a relapse of his malaria.
-The next month it was rheumatism, weakness and a general malaise so bad that he asked to be relieved of command.
-After that he was unable to ride his horse due to lumbago and sciatica until October. From 1862-65 he got around by ambulance and carriage more than on his own horse.
-Starting with October 1863 his angina symptoms, mainly in his back manifested themselves more frequently. Dysentery affected him through the rest of the war, particularly at the North Anna where he was confined to his tent and unable to execute his plan to bag part of the AoP.
-By December 1863 his hair had turned completely white.
-After the war the angina, malaria and rheumatism affected him almost daily, until he died of a stroke.
So by his mid-50s Lee was a medical mess.